WMG / Signs

The Aliens (General)

The aliens were no smarter than humans.

Everyone always assumes that just because a species is capable of interstellar travel, that means they must have unimaginably superior intellects. But this is a drastic case of Logical Fallacies. Human beings have been improving our inventions for eons and throughout all the thousands and thousands of years of constant technological advancements our brains have not evolved in intelligence to a very significant degree. In the amount of time it would probably take us to make it all the way to the point where we can travel to another galaxy—say, another few hundred years—we certainly still won't have reached that point. Probably not even in another few thousand. Especially not now that we're evolving less than before. An alien species analogous to our own in advancement would presumably be the same. That's how evolution works. When you get to a certain point, your brain doesn't need to evolve much more. Evolution is about survival in the wild, not technological convenience. You can't just automatically equate technological prowess with intelligence like it's an automatic given. Think, people. THINK. Don't assume. Think. These creatures are, if anything, less bright than humans—or at least than some of the smarter humans. The way they're hard wired, they seem to be better at long term planning than short term problem solving. They can set up tricks and traps and invasions well enough, but when confronted with something they didn't expect they always seem to miss the frickin' obvious and they don't know how to deal with it. If they were as brilliant as everyone thinks being capable of interstellar travel magically automatically qualifies you as being then they wouldn't act in such a way. This isn't an inconsistency: rather, it is a more or less realistic depiction of how such a species may be on a strange new planet.

• Technically not entirely true. If they can make stuff, like starships or power armor, that doesn't make them smart, but they also used starships, so they understand (at least) basic principles of mechanics. They seem to understand human psychology when they take hostages. Like monkeys. Stupid - yeah, but not as stupid to be incapable of making power armor suits and using them. Yet they fail...
  • The ones who built the starships, and the ones who fly them, are the ones who understand at least basic principles of mechanics. The ones who were down on earth might actually just be cannon fodder. Or to put it another way, majority of us don't know how to put together an airconditioning unit, much less an airplane or space shuttle. Why should they?
    • Why would they have sent down cannon fodder so dim they can't get past a locked door? What did they expect would happen? Do the smart aliens enjoy watching the dumb aliens get beaten up by primitive humans with baseball bats and glasses of water?
• Actually any species advanced enough to invent Interstellar travel will have modified their genome to increase intelligence. Its discussed in Stephen Hawking's Universe in a Nutshell. Artificial wombs would have to be used however as the increased brain mass would make normal childbirth impossible.
  • No, just no. Hawkings pet beliefs about about aliens are hardly more credible than anyone else's.
  • What if they had ethical concerns about that huh? Like, say, our own society would have?
  • Or they realised it was just unnecessary and economically unsound? Like our society would have if it were more cynical?
• Our intelligence has not improved, no. But our knowledge has increased. And we have, in fact, become more intelligent by proxy. We do not become more intelligent, but our machines can, and have.
  • You don't even need sapient AI. By the point you have starships that can go to another star system any smartphone would be able to tell this invasion plan is full of holes.

The aliens we see are mass-produced "grunts", and the important aliens were still in space observing how they handled the strange planet.

Since the grunts could handle neither the atmosphere nor the hostile locals (nor the primitive door technology), the alien leaders decided not to invade, or at worst to retreat and figure out what to do next.

The aliens were refugees!

Their homeworld underwent some catastrophe that nearly wiped them out. What few survivors there were packed themselves into ships and wandered to the nearest inhabited world. They only picked a planet with oceans of poison because they were desperate. They clearly announced their presence and came unarmed and unarmored. The crop circles were universal signs of "Help us, we're starving. Can you spare some food?" Humans, bastards that we are, tried to kill the people who need us! Sure, it looked like they were gassing and abducting humans, but they were just trying to hug us and share their alien cocaine.

• Or, when we so cruelly ignored their begging for food, they decided we were nonsentient and decided to treat us as food. (They make a mean jerky.)
• This sounds an awful lot like the plot to Alien Nation.
• Unfortunately, if this were the case, we probably couldn't help them — almost all our food contains water. And the I'm a Humanitarian thing probably wouldn't work either.

The Aliens were created on Earth as part of a Terran plot.

An intergalactic invasion is so incredibly expensive that any land, resource, or slaves one would capture would not recoup your losses. The only resource one could garner at a profit, information, is clearly not what the aliens want. Conversely, as portrayed in Watchmen and half a thousand other sources, the best way to unify the Earth is to create an extraterrestrial threat.

The aliens are incredibly unprepared for an invasion. Therefore, they were bred on Earth as part of a Gambit Roulette by some organization to create a one world government or some other lofty goal. There was nothing more to it than genetic engineering, puppetry, bribery, and sophisticated light shows.

• Yeah, it's the "best" way... just like how the U.S., Russia, China, France, etc. all put aside our differences to battle our common enemies in World War II. And afterward we all stayed friends and held hands and sang Kumbaya. Oh, wait...
  • Yep, we all know Hitler was an extraterrestrial. Someone decided to whip up another one...
  • Well, I think the idea is that the threat should persist indefinitely, thereby keeping everyone constantly united and fighting against it.
• And all this was orchestrated by the smartest man on Earth.
• No. It's all just a ploy by the soda companies to sell more soda! Or perhaps more Dasani water.

The aliens are from another dimension, not outer space.

What else could possibly explain their complete lack of preparation or equipment for landing on a mostly toxic planet? They are primitives who stumbled through a portal.

• Hmm, from another world, seemingly supernatural powers, water harms them... witches from The Wizard of Oz, anyone?
  • What, you mean with the little girl in the sparkly red shoes? And the guy who's scared of everything, and the guy who isn't in touch with his own emotions, and the guy who's smarter than he looks? Nah, couldn't be The Wizard of Oz...
• Primitives with invisibility-capable spaceships?
  • That isn't an invisible spaceship, it's alien hoodoo magic.

The aliens we see are the remnants of the splicers from Rapture.

The allergy to water is one of many possible results of the long-term genetic damage they did to themselves with the constant splicing, as is their appearance. It also explains how they got on this planet in such large numbers without someone noticing and gives them a proper motive for wanting to capture a bunch of people: ADAM.

• Problems with this: Rapture itself is a leaky underwater facility, which would've been likely to kill anyone unfortunate enough to have an allergy to water - though admittedly, that would make a strong incentive to leave. And BioShock was released well after the film, which means M. Night Shyamalan must be the precog he tried to tell us he was in Lady in the Water.
  • We will pay for laughing him off. He was our best hope to prevent us from being alien snack food.

The aliens are just plain stupid.

This is why they invade a planet full of poisonous chemicals with no weapons, armor, or reconnaissance. They are incapable of any invasion strategy other than "Hurr, hurr, let's land on that planet and beat them up!'' because they are stupid. They just stole their advanced technology from smarter aliens.

• It's Beavis And Butthead: The Alien Version. "Uhh huh huh... Let's take dad's spaceship for a joyride to the place they told us never to go!"
• Or their smarter ancestors made the spaceships a la Idiocracy. This is their version of suburban sprawl. And the next moon mission is gonna prove deadly for the astronauts.
• My God, Bill Hicks was right all along.
• This is actually the best hypothesis, as most of the rest could be rephrased as this. Smart aliens would use proper weapons or communications, environmental suits, spectrometers etc., or they would just synthesize anything they want.

The aliens were Criminals

They had been given life sentances, but were told that if they spearheaded the invasion they would be pardoned. The alien government knew they would all be killed.

The "Aliens" were not sentient at all - they were just smart animals.

The real aliens were shipping some fragile space monkeys to the galactic preserve. Unfortunately, due to an error in the delivery form, they were unloaded on the wrong planet.

The aliens weren’t naked.

They were completely covered in bio-mechanical suits (hence no visible genitalia). The suits were green either from being powered in a way similar to photosynthesis or by having a high copper content (which turns green due to oxidization). The suits, while capable of keeping the creatures safe from breathing in the water vapour in our air, were (unfortunately for the aliens) not able to stand up to liquid water. The one that attacked the Hess home was not killed directly by the water and/or blunt force trauma but, between Merrill’s hits and the water, caused the bio-mechanical suit to malfunction and tears in it leaked in the vapour rich air which seeped into its lungs causing asphyxiation.

• This theory might hold more weight upon further inspection. No mechanical technology is shown to be used by the aliens, and organic alien suits have precedence in Independence Day, so it wouldn't be too far fetched in an alien movie. I know one movie is not the other, but let's suppose it for this theory. They could be using these organic biosuits for camouflage, nerve gas delivery, and general body protection including respiration as noted by the troper above. We see no rayguns or other mechanical technology to hint that their technology is anything other than organic. Their ship may even be organic for all we know. If this were true, maybe the aliens were harvesting humans to assimilate human biochemistry into their organic technology, eventually allowing them to live in a water rich environment.

The aliens are The Buggers.

Signs is a prequel to Ender's Game.The aliens communicate through bug-like sounds, and they have a hive mind, which explains why they didn't have water protection since they didn't value their lives. Also, their poison neutralizes the harmful effect of water, making the humans harvestable.

The aliens created the DHMO hoax after the movie

only in this case it wasn't exactly a hoax but a way of using our scientific illiteracy against us. hacking into the interenet (our just casually creating their own site) they would gain the support of environmentalist groups which would eventually gain a lot of support and eventually ban the "harmful" chemical and allow them to invade easily, with the added bonus of the human population being wiped out from lack of hydration, the aliens would then colonize the planet.... at least that's how they thought it would turn out, naturally one of the cleverer of the 6 billion monkeys caught on and exposed the "hoax". as for why the aliens thought this would work well, they basically came to a planet made up of 80% liquid death, they're not particularly the brightest star in the galaxy

The aliens were drunk

They were having some wild party (hence naked), but got locked out from their spaceship without keys. The water thing? Alien hangovers are that bad.

The aliens were committing suicide.

Like Suicide by Cop, except it was Suicide By Invading Watery Planet And Getting The Natives To Kill You With It.

• Even better: mass ritual suicide. The crop circles are sacred markings they make for the ritual. They then descend, hoping to be dissolved to enable them to reach the highest heaven after death.

The aliens were genetic experiments gone wrong who had escaped their captivity while in hyperspace, killed their captors, and ended up near earth.

This explains not only their incredibly ill-planned "invasion", but it explains their freakish powers, odd weaknesses, irrational but scary behavior, and lack of any visible tools or clothes. This actually makes the fact that they acted more like horror movie monsters than any sort of force quite logical— they WERE monsters.

The Aliens weren't Aliens. They were demons.

I'm actually surprised that this one wasn't said already. It may take a bit of background knowledge of Aliens and Demons, particular Abductions. Bringing a little real world logic into this (bad idea? maybe.) but most (probably all) stories of Alien Abductions are actually the result of Sleep Paralysis. Back when humanity didn't recognize the concept of Aliens, people STILL had Sleep Paralysis, but they thought they were instead being tortured or "abducted" by Demons. There's little practical difference, at least to the "Abductee". Strange Lights in the sky have also historically been the result of Demons or something spiritual, until the modern age, where we began to attribute them to Aliens. Take into account that Water, in particular Holy Water, has been a consistent weakness of Demons throughout theological history, and not being able to enter someones home, while normally connected to Vampires, is also a common theme. Really, it all makes sense if you think of it like this. These "Aliens" have no technology that we see (that i remember), We never see their "Spaceships" aside from a few lights in the sky, which could simply be the means of which they enter our reality. They seem to have no greater goal than to terrorize humanity. Take into account that main character is a lapsed priest, which is also very common in stories featuring Demonic Antagonists, and suddenly it all seems quite obvious. If you're wondering, though "Why did the people in the movie call them aliens" well, what exactly would you call them? the Popular consciousness, in both our reality and the movie, simply favors a more Sci-Fi explanation.

• Furthering this WMG, crop circles, and random dead livestock have also been attributed to demons in the past.
• This also explains all the problems with water being their weakness. If the demons were put on Earth as a test of faith (i.e. God gave every faithful-at-some-point person a clue to help them against the demons, sometimes killing their loved ones to do it), it makes sense that these demons wouldn't be killed by anything that could be rationally guessed.
  • ... why? He didn't give us brains to weight our heads.
  • The only time water was shown to burn the aliens was from stagnant water in the house of a lapsed by never formally defrocked priest. It's Holy Water.
• This theory is further supported by the news reports of the battle turning around in the middle east. A area not known for its abundant water but plenty of religion.

The bipedal aliens were made to send a message to Man

It's not likely that that a race that evolved on another planet would be as humanlike as the aliens in Signs. The starship builders created humanlike life forms, and made them water soluble so that they'd die quickly. The crop circles and the invaders were meant to communicate something to Man. We don't understand the message because the Starship Builders' culture is too alien for us.

The aliens were genetically-engineered slaves on the run from their Masters, and were only making a provisioning stop on Earth

Morgan mentions when reading his book that space-travelling aliens would be physically small, with large heads, because their intelligence would overrule the evolutionary need for physical strength. However, the aliens that invade are physically large, with proportionally average heads. It's probable that these aliens were genetically-engineered slaves created by the smaller, more intelligent aliens (presumably The Greys) that Morgan's book refers to. This would explain everything. The aliens don't seem particularly intelligent, despite having spaceships, because they didn't build the spaceships, they just stole them. They are naked and unarmed because they never had clothes and weapons to begin with, having escaped their planet in a hurry. The guy on the radio at the end says, in exact words, : "people say they came here to take over the planet. That's bull. My friend and I saw them. They poisoned his family and dragged them away. This was a raid. They came here for us; to harvest us. We're lucky as hell they're leaving." It could not possibly be made more clear to us that the aliens weren't trying to take over the planet; they came here to perform a mass abduction, presumably as food for the rest of their journey or for the use of slave labour to build a colony wherever they chose to settle. It was just a stopover while they continued on the run from their Masters. Being unarmed, their method of attack relied on stealth and the element of surprise. Though it was physically possible for them to break down doors, being unarmed, they knew that was a bad idea, because the humans would easily be able to defend themselves. That is why they were snooping around Graham's house the nights before the invasion. They were looking for alternate entry points to the house that they could use to ambush the family on the night of the invasion. As Graham realizes when they are in the basement, the aliens aren't actually trying to break through the door, they are just banging on it to make noise as a distraction, while the other aliens sneak in through the alternate entrances (the attic door and the coal chute) which they had scouted out previously. Once the family blocked both entrances to the basement, the aliens gave up because the element of surprise was now gone, and they didn't want to risk just barging through the door, because they knew the humans were probably prepared to defend themselves. In this sense, the aliens did not actually lose the invasion; they collected the number of humans they deemed necessary and left. The improbable water weakness was probably a trait genetically engineered into them by their Masters to make them easy to defeat in case they tried to rebel. The aliens did take whatever precautions were possible to avoid it (Ray mentions there are no crop circles near large bodies of water).

The Invasion

The invasion force was never meant to succeed.

The aliens sent to invade were the backwards hillbilly species of the universe, stupid, fragile, and relatively useless. The real point was to test humanity, to ensure that our apparent technological level was the limit of our technology by seeing how they responded to a potential invasion. After all you don't want to go into what you think is a primitive society with chemical propelent weapons and find out they have laser and plasma based weapons that are only available to the military.

So they dump the galaxies idiots on our doorstep with a mandate to raise hell and they will be richly rewarded, on the off chance they succeed, and then sit back to see what happens. Then if the earth proves capable of fending off the idiots they start figuring the level of risk based on the results they observed to mounting a real full scale invasion.

The aliens were just showing off. Invasion was not their goal.

Any race capable of interstellar travel in spacecraft that can turn invisible ought to be smart enough to have proper weapons and strategies for invading Earth. Their strategy was woefully inadequate, and their weapons were nonexistent; therefore, invasion wasn't their goal.

Things the aliens may have been doing other than invading:

1. Hunting humans for sport.
2. Undergoing a manhood alienhood trial.
3. Messing with a primitive planet on a dare.

Whatever they were doing, the aliens intentionally handicapped themselves—choosing a planet two-thirds covered in water and limiting themselves to hand-to-hand combat—to show off how tough they were.

The aliens were trying to make a peaceful First Contact.

They were just lousy at it.

Think about it. They went to a planet that was covered in poison with no protective gear and with the worst invasion strategy ever. The kidnappings were retaliation for attacking their ambassadors.

• Or their First Contact manners are similar to the Minbari's.
  "Open the Gunports, nothing can go wrong!"
• Just like the South Park pilot:
  Alien: We have experimented with all the beings of Earth, and we have learned that you are the most intelligent and wise.
  Cow: Why did you turn some of us inside out?
  Alien: Oh, that was Carl's fault. He's new.
  Alien (Carl): Yeah, sorry about that, my bad!

The alien holding Morgan wasn't holding him hostage - he was giving the kid medicine.

First of all, if these aliens were smart enough to have cloakable transport, have tested lifeforms (since animals share quite a few spots of our human genome map), and know well enough to avoid water, who's to say they don't know our biology? The alien was surrounded and weak anyway, so holding a hostage would be a dumb move. Instead, he tried to appease by trying to resuscitate Morgan, and use sign language to communicate his speci's true intent. Of course, dealing with Mad Max here was a VERY bad idea. Way to go, Mel Gibson.

The Aliens were after some specialized resource, and actually won.

The aliens weren't here to conquer the earth; they were here for resources. Something in our bodies is valuable to them. It's like miners going into a mine to dig for gems or coal. There's a known risk of methane gas for miners, and a known risk of water in its many forms for the aliens. Chances are some of the miners, and some of the aliens, will die; but the payoff is high enough to make it worth the risk. So yeah, a couple died, (at least one) unfortunate, but they knew the risks when they signed on, and the rest made it out with what they came for.

The aliens lost a ship carrying a VERY important thing at Roswell

They didn't know where the ship was hidden on the planet, so they invaded everywhere at once. Once they got the missing thing (treasure, a resource, whatever) from Area 51, they sent out the signal to go home.

The important aliens are far more powerful, and they destroy the Earth after the movie is over.

The weak aliens were a test to see if we were Xenophobic. If we had made peace with them, they would have brought us into an alliance.

The Aliens were invading Earth FOR the water.

Think about it. If the aliens are vulnerable to water, then they likely did not evolve on a planet with water. Water isn't exactly a common molecule in space. They want the water as a deadly weapon they can use against their kin. The Signs were business proposals to obtain the water peacefully: They wouldn't want to divert resources from fighting their enemies. (That's also why the invasion force is so small.) When that failed — well, humans are mostly water, so they'll separate us into water and human jerky.

• Why not mine some comets, or an Ice World like Europa?
  • Because of the last WMG - they're idiots.
  • They are mining comets, but comets are a lot smaller than Earth is. They can't mine Europa because there's no way for them to get leverage — there's no place on the surface of that moon that isn't outright water. We can walk on black Hawaiian lava if we're willing to melt our sneakers, but we can't touch the red lava. For someone who can't touch water, the difference between farm fields and ice balls is similar.
  • If they wanted water, even if it absolutely had to be from Earth, why bother getting out of the ship at all? They could just fly in over the middle of the Pacific, lower a pipe, and pump the hold full. Or if it had to be fresh water, they could go in over one of the ice caps and use a crane. There's no need to expose fragile alien flesh to the horrible death world in the first place.
• Water is actually the second most common molecule in the universe.
  • Not in their corner of it.
  • Water is H2O. Hydrogen is actually just a proton and electron. It is everywhere, it is produced by stars and radioactive nuclei. Lots of oxygen was made when population III stars gone nova, which spread across universe - there are no pop. III stars now, so everything is made of them. That means lots of oxygen and even more hydrogen everywhere.

The Aliens are on the run from a much MUCH scarier race.

They just stopped by earth for a bite to eat...they were running out of food, and desperate enough to head towards Earth for food. They sent a few agents ahead to plan the attack, thus, the crop circles. Oh, did I mention the above mentioned "Much scarier race" is heading for Earth, and won't be as easily repelled?

• Hungry aliens attacking humans, and later a much more effective species that hunts them shows up? Now, if the xenomorphs show up, the predators' and xenomorphs' blood will react and neutralize into water, which is harmful to the Signs aliens, so all we'd need to fight them off is a storm of firework arrows for shrapnel.

The Aliens needed human slave labor.

The radio said that the aliens seemed more interested in abductions than all-out combat. If they found a world with resources they needed but which had large amounts of water present, they'd need either major protective equipment or a slave species to harvest the resources.

The aliens were just idiots screwing around.

Aliens Bob and George were travelling the galaxy, when Bob spied a peculiar planet.

Bob: "Hey George, let's go down there and run around naked so we can scare the natives who've never encountered life from other planets."
George (the more cautious of the two, pauses): "I don't know. That planet is covered in acid."
Bob: "Don't be a pussy."
George (beginning to be quite annoyed at Bob's remarks, agrees): "Hey, I learned this trick from Steve that drawing circles in their food supplies really freaks them out."

• Sounds like the same kind of guys that Ford Prefect hitched a ride with when coming to research Earth for the Guide.

The invasion was actually the result of an Interstellar Uriah Gambit

What better way to create a suicide mission than to send the underling to a planet covered (about 75%) in what will literally eat then him/her/it alive. The other troops were probably recruited from prisons, asylums and amongst the dregs of their society. How can their equivalent of coroners complain when there are no remains (melting away during the first rain storm)? Those in charge knew; the troops were told they were to procure Di-hydrogen-monoxide by any means necessary. Society was told that they were tragic losses while on an exploration mission to a deadly planet with barbaric inhabitants.

• Does that mean the Aliens' leaders essentially did to them what the Irkins did to ZIM?

The aliens were in a similar position to the Golgafrinchim B ship.

Much like the B ship, the aliens in the movie are the useless portion of their species. Wanting to eliminate the incompetent members of their race, the alien species made a volunteer Alien Invasion of water based planets, knowing only the truly stupid would volunteer.

The Tet in Oblivion (2013) was the Aliens' second try at invasion

Having learned from their embarrassing failure in this film, they sent an autonomous force to remove all the water from the earth and hopefully mop up the locals too before they colonized the planet.

The Weakness

The aliens were damaged by chemicals in the water, not the water itself.

There's plenty of crap in tap water other than good ol' H20.

• Death by Flouride isn't much better.
• Death by Chlorine is good, though.
  • Or herbicide! (Our protagonist lives out in the country.)
  • It did take place in rural Pennsylvania. Hydrofracking chemicals aren't completely identified.
• Flouride seems like the biggest possible culprit, the aliens do have skin with a coloration similar to solidified chlorine. If there skin is chlorine based rather then what humans have it would react violently with liquid containing Flouride. Since Flouride isn't naturally found in such high levels in fluids, after all it's natural state is usually as solid crystals and mineral deposits.
  • Our skin is made of carbon, nitrogen, oxygen, hydrogen and sulfur and it's not black with clear and yellow streaks. Element chlorine would react with fluorides (releasing fluorine gas, which is unpleasant), but chlorine compounds wouldn't.

The Aliens didn't KNOW that water harmed them

Water isn't naturally blue. Why should the aliens think that the blue pieces of Earth are water? They don't have water on their planet, or not much of it, and they clearly didn't send out any unaliened craft to get the composition of Earth before they invaded. It's entirely possible that they never encountered a watery planet in their voyages and didn't realize what water does. Maybe they never even visited another world before (we really overestimated how much dust the surface of the moon had, after all).

That could have been their first encounter with water. Hydrogen may be the most common element in the universe, but oxygen is a good deal rarer. Or maybe they're only hurt by water above a certain concentration; their breathing on Earth is a lucky coincidence they discovered by trial and error.

• That does not change the fact that water is the most common chemical compound in the observable universe, second in sheer mass only to stars.
• Yet more evidence for the "aliens are stupid" theory.

The Aliens suffer from a negative reaction to certain ions of water.

Water is not a poison to the aliens, they simply suffer from something similar to aquagenic urticaria, a real world disease where people suffer from a horrible skin response to certain ions in water. This still doesn't explain why they came to a world three quarters covered by water, but hey, it's just a movie.

Water in and of itself is not harmful to the Aliens.

Rather, there is something in the water that harms them. The film has some foreshadowing to support this idea, with the main character's daughter refusing to drink the water because "it has amoebas in it". Some kind of bacteria or virus found in unfiltered tap water (remember, the film is set on a farm which probably has a well rather than an urban water supply) can literally eat the aliens alive.

Not all aliens are allergic to water.

We only see the one alien reacting badly to water. Yes, people in the Middle East fought them off - but it never says they used water. Yes, the veterinarian said they chose landing sites away from water - that doesn't make them allergic necessarily, just not fond of water. Perhaps the one alien that invaded the Hess home was some poor schmuck who happened to have a seriously inconvenient allergy - like humans allergic to peanuts, the sun, vitamins, etc.

Water is not lethal to the aliens.

Perhaps it just hurts them: as we see the skin burns off the alien when touched by water. Want to know what actually killed him? Perhaps it was something to do with Merill beating the SHIT out of him.

• Could be a combination of the two.

Firefighters end up on the front lines.

Firefighters vs aliens. Teh awesome cannot be more obvious.

• After the humans win, they erect a statue to commemorate the victory. The statue depicts a lone firefighter wearing a gas-mask, fire axe in one hand, severed alien head in the other.
  • So, the Pyro is just training? I knew his insane beliefs meant something!

There's nothing in the water that kills aliens.

Their skin contains large quantities of Sodium. The water reacts with the sodium and turns it into caustic soda, a highly corrosive base. That smoke where the water touched the alien's skin looked a lot like sodium reacting with water.

• Again - sodium reacts with lots of things. It's not really viable for building anything.

The aliens were specifically hurt by fresh water

They saw most of the planet was covered in salt water and assumed that all liquid on the planet was similar.

It's the bacteria in the water that harms the aliens, not the water itself

After all, the reason for the girl leaving half-finished glasses of water all around the house was exactly that, she thought it had dangerous bacteria on them.

The aliens are damaged by water because they aren't carbon-based

Being poisoned by water is something improbable for any carbon-based life form. But what's less widely known is that there are several theoretical alternative biochemistries— silicon is the best-known— that would not require water at all. Indeed, a silicon-based life-form would find water toxic, and instead use ammonia as its solvent. If the aliens find water in any quantity to be lethal, then their biochemistry must be based on an element other than carbon, such as silicon. It's possible that, in the Signs universe, silicon-based life is actually the norm, hence why the aliens didn't expect to find a planet whose environment was so toxic to them.

Theology

Graham was right: there were no psychic powers, and everything is thanks to God.

He just doesn't notice that God Is Evil.

The Aliens are only hurt by holy water, or at least water handled by a holy person.

This would explain why they die when a priest throws water at them, but they weren't afraid to invade a planet full of water because it wasn't naturally poisonous.

• This could mean the aliens are demons.
• However the news did mention the aliens not appearing around large masses of water, so it's not just holy water.
  • Though it's possible that beings with a weakness to holy water would just avoid all large bodies of water as a precaution, since there's no guarantee that they would have any way of knowing which water was actually blessed until they were actually doused with it (which could potentially kill them).
  • I've always been inclined to believe this theory, but it's important to note that it would require a rather looser definition of "holy man" (or "holy woman") than most works tend to give. It could mean that some people are just naturally anointed by the Divine without their knowledge, for reasons beyond their comprehension.
  • The news never says that. It's only Ray who says that.
• Or, alternately, there is no minimal dilution of holy water, and enough of it has gone down the drain into rivers and oceans that every drop of water contains some of it. Which can also explain the resistance to water vapor...it only counts if it's holy water. Holy water vapor and holy ice don't count, it's a supernatural rule, it doesn't have to make sense.
• And it's possible they didn't quite understand this problem until they got here, which would explain why they came, but then a few of them touched water and realized what was going on.
• If we are going to accept that in the movie God exists and intervened to save the family, it's also perfectly possible that he also blessed ALL the water on earth so we could fight the demon invasion.

God Is Evil

It's extremely difficult to think otherwise here. If we're to believe the final five minutes of the film, we accept that God killed Graham Hess' wife (traumatizing an Indian veterinarian in the process), gave his son asthma, made his daughter neurotic about her drinking water, and, last but not least, sent aliens to abduct half the population of the Earth...so Graham's brother could take advantage of a weakness already established earlier in the film and, more importantly, so He could save Hess' son from the asthma he gave him in the first place. Which, in the end, convinces Graham to become a priest again.

• From a Christian theological view point. God does not cause any sort of evil, though He can work any bad situation to good. God doesn't break a leg to fix a paper cut. From a Maltheist theological viewpoint - yes, God really is that much of a dick.
• God didn't send the aliens, He just set things up so Graham's family could be saved. (Granted, sans wife, but it is possible that her death had to do with something besides the alien invasion. Possibly him just being a dick.)
• Remember that it wasn't just Graham's faith that saved him, it was the faith of the Middle Easterners that saved the entire frickin' world. (The primitive method of defeating evil the newscast referred to obviously must have been holy water.)
• This is basically a heavily softened (his kids live and God doesn't yell at him for complaining) retelling of Job. Whether it counts as evil or not depends on if you grant Omniscient Morality License and nothing else.
• Nowhere is it etched in stone that the entire invasion takes place solely for Graham's sake. There are generally numerous reasons why things happen. That's part of the whole point of there being no coincidences: everything is interconnected. The world doesn't revolve around one person, you know.
  • Grahm's wife certainly died to save their son from an alien invasion though, which is still a dick move on God's part. As if the brother couldn't figure out to hit an alien with a baseball bat if that hadn't been her dying words.
  • It's easy to think it was all solely for the purpose of restoring Graham's faith, since he's the main character and all, but really, if you think about it, it's very likely the invasion would provoke a similar reaction across the world once the full implications became clear. The creatures eat Humans, which are 60% water, yet water melts them. It makes no scientific sense. And what do you call something that makes no scientific sense but it happens anyway? A miracle.
  • Not necessarily (does love make scientific sense?) - also, the whole losing/regaining faith is very... Hollywood Atheist and Evil Stole My Faith sort of missing the point.

God Is Good

God did not kill Graham's wife so she could pass on a message. In the scene, when Graham is talking with her wife as she is dying at one point she says to "Tell Graham" which seems a little odd since she is talking to Graham at the time and she did recognize him when he first came up to the car. What if at that moment, she wasn't talking to Graham, but to God? Each "Tell so and so" message was directed at the Big Guy as the last wish of a dying a woman who wanted to protect her family. And, while God doesn't cause evil, He can bring good from evil, and since He doesn't exist in Time per say and can see the whole shebang at once, he granted her dying wish and allowed her to pass on just the right words to Graham to protect him and his family in their coming time of need. It's not so much that God gave the son asthma or the daughter her neurosis about water as He could see from the outside how He could use all these things to help with a little hint or push here or there.

• Shyamalan's character said he felt that the accident could only have been caused by God. This could a Red Herring (and projection of guilt on this character's part), but it does sound like the death was God's doing.

Other

The kids' mother was part alien

Hence Bo's aethereal looks, "premature" smiling, precognition (which we know she inherited from her mom: "Swing away...", etc.), and dislike of water. She's at least half human, so it doesn't harm her; she just feels like it isn't clean.

This also might explain why Morgan is asthmatic and generally sickly throughout the film, but after one shot of alien nasal-spray and a quick nap clears right up (possibly leading to the most energetic reading of "Dad?" in the entire movie).

The entire invasion might be a retrieval operation for hybrids. After all, the radio reports did say they were dragging off people. The spacemen might have mistaken the humans' attempts at saving their loved ones for those of kidnappers grasping at their hostages, and acted accordingly.

• You fail biology forever.
  • Wait, you expect legitimate biology from an M. Night Shyamalan movie?

Graham's wife and Bo were both psychic; Morgan knows this, but keeps it secret from his dad

Graham's wife had a psychic vision, which is why she knew to tell Merrill to swing away. Bo inherited her gift. She is paranoid about the water because she knows it is harmful to the aliens, she has a bad dream shortly before the invasion begins, and she says "I dreamed this" during Morgan's asthma attack. Morgan is aware of her abilities. During the telescope scene, when she says she's worried, he asks her "did you have one of your dreams again?"; the "dreams" he is referring to are actually visions. However, Morgan keeps this secret from his father because he knows his father's loss of faith would cause him to discourage them from believing in Bo's visions. So at the dinner scene, he refers to Bo's vision as "a bad feeling" so that his father won't question it, but Bo clarifies that it was a "dream", or vision.

• This could also explain what Morgan meant by "you let mom die." Maybe Bo had a vision that Colleen was going to be hit by a truck, but Graham dismissed it as a dream and didn't stop her from going for a walk that night. Graham then went into denial about heavenly "signs" because he felt guilty over her death. And it would explain Morgan's resentment when Graham once again refuses to heed Bo's warning during the dinner scene.

The "invasion" is really Graham's dream

The alien invasion is really a dream Graham is having as he mentally wrestles with his loss of faith after his wife dies. This would seemingly explain odd scenes like the illustration in Morgan's book that shows people who look like Graham and his children lying dead outside a burning house, the strange conversation with the army recruiter which sounds like something from a David Lynch film, and the alien's weaknesses like water and the inability to open doors. It's all dream logic at work.

Signs and Unbreakable take place in the same universe.

Mr. Glass wanted to find a superhero because he knew the aliens were coming.

• Too bad the one he found was already part alien, what with the water weakness an' all...

The entire movie was a more realistic take on the same concept as Invader Zim.

The alien grunts weren't all that bright, and Earth was obviously the last planet their species should ever want to invade. Hence, the aliens we see in the movie were a group of annoying idiots their superiors wanted to get rid of by sending them on a "Secret Mission" to an acidic Deathworld.

The film was a commentary on prejudice, racism, and cultural invasion

This is my true interpretation of the film, and I have never seen this echoed on any website or with anyone I have discussed this with so I'm sharing it here. Signs was about ignorant prejudice that devolves into mass panic. We see the aliens messing with the farmhouse, but nothing they do is truly malevolent. Keep in mind that they are from another planet far away, and this might be their first contact with an intelligent species. They might not even perceive humans as having intelligence comparable to their own. Even though we build cities and farm houses they might think of it as an ant makes an anthill.

Next we see the invasion. The news program shows an alien peeking into the window of a children's birthday party. The alien is causing no harm here, it is only curious. Sure, the news stations claim there have been reports of abductions, but we do not actually see them occurring. This is just wild rumor and mass panic by the general public in the face of a cultural invasion. We see the kids at the farm house hiding in the closet, wearing tinfoil hats, and obsessively watching the news because they are driven by ignorance to panic and take irrational actions.

At Shyamalan's house, an alien enters his home and he locks it in the pantry. Again, from the alien's perspective, this is probably not a malevolent act. The aliens have interplanetary travel, they could do better than send one unarmed alien into his house if they wanted to cause him harm. In return for trying to make contact, the poor guy gets locked in the pantry. Then Mel Gibson goes in there, and the terrified alien reaches under the door to reach for help. In a panic, Gibson slices off one of its fingers.

At the end of the film, the young boy has an asthma attack and loses consciousness. The family then sees on the news that the aliens are leaving Earth en masse because water is poisonous to them. Next, a lone alien breaks into the house and the family sees it has the unconscious boy cradled in its arms. A closer look reveals that the alien is missing a finger. It is the one from the pantry, left behind by its own people on a strange world. And yet, when faced with the one who cut of its finger, it still has the kindness of heart to heal the boy by spraying a mist in his face. Gibson then tells his brother to brutally beat the alien with a baseball bat, which he gladly does. The unarmed alien offers no resistance. Shortly after, the young boy awakes, thanks to the alien's antidote. Gibson and the family show absolutely no remorse for the brutal murder of the one who saved the boy. In their ignorance, they interpreted the alien's act of kindness and forgiveness as an act of aggression, and they killed him simply because he wasn't human.

The film is actually a commentary on religion.

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