Near the end of the film, Drax cheerily calls Gamora "green whore". When they were in prison, the other inmates called Gamora (among other things) "whore". Being excessively literal, Drax has difficulty with insults like that, and likely genuinely thinks Gamora is a prostitute and has no idea that "whore" is a pejorative term.
Alternatively, knowing she is Thano's favored daughter and assassin, he interprets whore as a compliment and literal description of her, not knowing that it doesn't describe a badass.
Groot's survival. He is at heart a plant, and like any plant, he can be regrown from just a cutting so long as it is still alive, and the best part is that since he is a plant anything grown from him will be an exact clone. Depending on how Groot's memories and personality are stored he may even be exactly the same. Not to mention, the twig absorbed some of the Infinity Stone's power...
At the end of the movie, Groot is seen growing faster when he is exposed to music - just as real plants have been known to do.
During Thor 2, it was unclear why the Asgardians didn't make any effort to use the Aether against the Dark Elves, or at least the Tesseract (which they do understand). After watching people be torn apart simply by touching an Infinity Stone (and the resulting explosion), it becomes very clear why that was never an option.
Rocket finds stealing other people's cybernetic implants like a leg or eye amusing. It's because he's the walking result of cybernetic implants.
Near the end, the Infinity Gem's power was divided among the whole team. Rocket was holding one of Groot's twigs.
The Collector mentioned earlier that groups have tried to hold and Infinity Gem's power before, but they never survived for long. Every Guardian is something unique: Star Lord's father was some ancient being (who his mother mistook for an angel), Gamora is a cybernetic assassin, enhanced by Thanos (who wants to recover all the gems), Drax has a hardcore focus and sense of duty, Rocket survived being taken apart and rebuilt, and Groot is a Floral Colossus, something so rare and old that not even the Collector knew what he was.
When Yondu opens the orb to find the Troll Doll. Star Lord, quite literally, trolled him... and did it with a surprisingly sensitive gift, given Yondu's fondness for knickknacks. Given that Peter was raised by Yondu, Yondu probably saw it several times while Quill grew up. Yondu knew that this was a heartfelt gift.
A meta example: All the songs on Peter's "Awesome Mix" cassette are from The Seventies, the decade Peter's mom was a teenager. It's also when most of the characters in the movie were created in the comics (Star-Lord, Gamora, Rocket, Drax, Thanos, the Nova Corps and Howard the Duck).
Peter's mother called his father an "angel" at the beginning of the film. At the end, we learn that he is actually an alien. Now where else did someone think that aliens were angels? Indeed, "Come Sail Away" was made in the '70s, so Peter's mom would likely have heard it.
Why wasn't Yondu offended by the troll doll inside the ball? Because he's been shown to have a love of collectible figurines, and this Earth-made troll doll is a unique artifact outside of Earth culture, making it extremely valuable.
When Starlord begins singing and dancing "Ooh Child" to distract Ronan, he actually stops and unnervingly demands to know what Starlord is doing. Ronan might have been so bothered because Thanos had continually referred to him as "boy".
All of the Guardians could be considered foils to each of The Avengers:
Groot on the other hand, is the team's nigh-invincible Juggernaut, much like The Hulk, except he's the mostcalm, collected and sensitive of the team. For bonus points, he also happens to be close friends with the above-mentioned Rocket.
Rocket is an accomplished thief who believes that any item that he wants more than its owner does should be rightfully his. Of course! It's in his nature. Raccoons are the thieves of the animal kingdom. (A lot of his other traits are also very raccoon-ish; he's good with his tiny little hands, he's very clever, and he's got an awful temper when pushed).
Adding to that, why does Yondu have a Southern accent? Because that's what his speech pattern sounds like to Peter's translator.
Further brilliance sets in when you realize why he can't fully translate Groot's speech: because Groot is from an exceedingly old and rare species (if Tivan has no clue what you are, you're definitely obscure) that speaks a Starfish Language, it's totally reasonable to assume that the device has no way to correctly translate his speech because it has no definitive record of the language, so it just does its best and winds up coming up with something that is roughly on the same level as Google Translate. "I am Groot" is nowhere near what he's actually saying, it's just that the language is entirely based around intonation rather than actual sentences, and since there's no record of the language in the translator's database, it just takes it at face value.
Even better, Rocket can understand Groot perfectly because his ears are more sensitive to sounds that normal people can't pick up on, so he's probably hearing a lot more in Groot's intonation than the rest, hence why he can pick up exactly what Groot's saying, rather than just relying on inflection and context.
It's entirely possible that, being a plant-person, Groot's language isn't entirely - or, perhaps, even mostly - based on vocalizations but scents. Which would make Rocket being the only one who understands Groot perfectly entirely logical too: he's the only one whose senses are both sensitive enough to pick up every scent Groot uses and with the experience to know what each one means. (Raccoon noses are much more sensitive than human ones, and Gamara and Dax - if they have noses as sensitive as Rocket's - don't have the knowledge they'd need to translate each scent.)
Yondu's grin at the troll doll. Sure, it's funny and he appreciates that. Sure, it's something he actually likes, so he appreciates that. And certainly you can say that since the Ravager's motto is "Steal from everyone" it's an appropriate bit of irony. But think of it this way. Quill is Yondu's adopted son: Yondu might be a crook and a hardass but he's presented as fair to his crew. Certainly neither one could really show traditional concern for each other. With that in mind, part of Quill's personal journey in the movie is about him coming of age and becoming his own man outside of the sphere of influence of his father - at the start of the movie, he's your typical teenager rebelling against his father. By the end, he has become his own man that his father (and his first lieutenant) respects. He has struck out on his own and formed his own family. So with that in mind, the gift of the troll doll and the manner in which it was given is an acknowledgement from Peter to Yondu - acknowledging the lessons of his father in a respectful way while also saying that he's no longer a little boy to be looked after. In this light, the gesture is actually very heartwarming. In this light, Yondu's smile isn't just one of humour but of pride in his adopted boy.
In the ending montage, we see Rhomann going home to his family. Note that this parallels the situations of two of the Guardians - he has a wife and daughter, like Drax, and he's a human (or Human Alien) while his wife and child are alien in appearance - the reverse of Peter's family.
The implication from Dey calling Rocket by his experiment names suggests that either most people don't know or don't care that he actually does have a name. All of the other Guardians call him Rocket even during their first meeting - which might have endeared them to him faster than usual since they basically weren't calling him a monster but an individual. This also makes it more heartwrenching at the climax. Saal, as he's about to die, just calls Rocket by that name. No experiment number, no monster type thing, just "Rocket".
Groot's abilities and fighting style and how they evolve over the course of the movie. At the start of the movie, he's apparently only been partnered with Rocket. So of course he wouldn't know how to brawl: Rocket's no brawler (willing, but not able) so Groot wouldn't have learned either and thus would have simply relied upon his natural abilities as a meat (wood?) shield - hence also his trouble restraining Gamora to begin with. But in each of his fight scenes later, he ends up mimicking one or more of his teammates as well as adding more to his move set, generally the one he's fighting along side. When fighting with Drax, he brawls. When fighting with Quill, he shows more finesse moves.
Despite the Soundtrack Dissonance, some of the songs playing over a certain scene have a thematic connection:
Peter listening to 10Cc's I'm Not In Love while waiting outside his dying mother's hospital room. The song has themes of denial and a fear of commitment, right before Peter refuses to hold his mother's hand out of fear of losing her. At the end of the song, the singer realizes he really is in love; in the film, right when Meredith passes, Peter immediately reaches for the love and warmth that just left him. It also has the refrain 'Big boys don't cry' being repeated in an ethereal voice, reflecting the fact that Peter needed to be strong for his mother but couldn't.
Redbone's Come and Get Your Love invites someone to indulge and take what they want and forget about the consequences, which is reveals Peter Quill's character and philosophy towards life.
Escape (The Pina Colada Song) plays during Peter Quill's escape from the Kyln.
David Bowie's Moonage Daydream has nonsensical lyrics and implies insanity, which fits Knowhere's insane and awesome appearance.
Fooled Around and Fell in Love by Elvin Bishop is about a Ladykiller in Love, and plays during a tender moment between Gamora and Peter. He selects the song himself. He probably pulled that exact same trick more than a few times before.
O-O-H Child by The Five Stairsteps plays during the Guardians' Darkest Hour when it looks like Ronan has won, and the Guardians indeed pull together to defeat him (due in no small part to Peter actually singing it out loud to confuse Ronan!).
Ain't No Mountain High Enough by Marvin Gaye and Tammi Terrell is not only a message of love from Meredith Quill to Peter, but also plays over the many relationships that had been formed/saved by the Guardians. It signifies the start of the Guardians as True Companions, it shows the family that the Guardians had inadvertently saved on Xandar, and it even reveals Yondu's paternal affection towards Peter as he proudly sees how much Peter took after him.
Nebula and Gamora:
There's a reason why Nebula behaves coldly towards Gamora. It was because she was always Thanos' favorite daughter. Nebula's behavior can be similar to that of a spoiled brat who was never seen as a favorite. In short, we are witnessing a genderbent space version of the relationship between Doctor Doofenshmirtz and his younger brother Roger.
Similarly, there's a parallel between Nebula and Ronan and the Guardians. Nebula and Ronan have grievences similar to the Guardians. Nebula like Gamora was tortured and forcibly transformed into a soldier for Thanos just like Gamora with terrible experiments done on her, just like Rocket. We know very little about Ronan beyond his speeches about how he loathes Xandar because his father and grandfather died in the war with Xandar, but we can assume being raised in a fanatical, war-like environment left its mark. You could even say Ronan is a Evil Counterpart to Quill in that regard, as both were not raised under the best of circumstances. What made the Guardians different from the villains was how they chose to cope with their losses: by giving a shit about other people and banding together to do something good.
Yondu's spent years telling Peter that the Ravagers wanted to eat him because Terrans are considered an oddity to the rest of the galaxy. By the end of the film we see that Yondu genuinely cares for Peter in a gruff, roundabout way and constantly threatening to let Peter be eaten can be seen as Yondu's way of preparing the young boy for the harshness of life on the fringes of galactic society.
Some people complained that Drax didn't express confusion when Quill, during his Rousing Speech, says they now have a second chance to "give a shit," since he's exceptionally Literal-Minded. Later during the plan to assault the Dark Aster, however, Drax remarks that he sees the Sakaarans as "paper people." Drax is beginning to understand figurative speech! Though as his Pre-Mortem One-Liner to Korath revealed, he still hasn't quite grasped its nuances.
Peter, unlike Drax and Gamora, never called Rocket "vermin" or "rodent." Having grown up as the only human among the Ravagers, he probably knows how it feels to be different and called derogatory names. To take it a step further, Rocket never called Peter humie to his face, further suggesting it's probably a racial slur, and once he has his breakdown and Peter shows sympathy for him, he never calls him it again, even to the other characters.
Every time a fight breaks out, or looks to break out, Peter is right in the middle doing his best to play mediator. Every time - unless there's no other way out, he's trying to avoid a fight. Now, imagine why this is - what his upbringing with the Ravagers must have been like for that to be his default response to a problem? Also doubles as Fridge Horror.
Yondu complaining about how disloyal Peter is when he didn't allow his crew to eat Peter when he was a kid. The two things we know about Peter's father are he's a jackass, and he might be powerful enough to wield an Infinity Stone. So, either Yondu's complaints are really a way of venting that he risked the ire of a very dangerous alien when he adopted Peter rather than bring him in, or they just became a lot funnier due to Skewed Priorities.
Rocket imitating the collectors “Milking the Giant Cow” hand gesture gets funnier if you release that given previous events, Rocket is still probably quite drunk at that stage. In fact, the beating up grass scene and the decision that the best way to rescue people is to threaten to blow up the ship they are on unless they are handed over in the next five seconds makes far more sense if you presume Rocket is still half cut.
What were the Dark Elves doing during their self-imposed exile before Thor: The Dark World? Hibernating. What's the captured Dark Elf doing in The Collector's emporium? Curled up, taking a nap.
Why would Groot lie to Rocket about drinking from the fountain? It's not like Groot has any problems with self-image or what not. He's lying because he's trying to mimick Rocket who in turn is trying to blend in as part of the job of finding fugitives. And what do regular plants do? They drink water. He was probably not shaking his head to say "No, I"m not drinking water" but rather "No, you don't get it. I'm pretending just like you!"
The movie's signature song is "Hooked On a Feeling", which was memorably used in Ally McBeal, where it accompanied a hallucination of a dancing baby. In retrospect, Guardians use of the song feels like foreshadowing of dancing baby!Groot.
What is Howard the Duck doing at the Collector's place? He's the only one from a dimension of duck-people to cross over into our universe. Sounds like a pretty rare collector's item to me.
When Rocket says he needs one of the guards' armbands to enact his plan to escape the Kyln, Gamora immediately volunteers. During the prison riot, she passes over several guards to target the one who'd abetted the vengeful prisoners trying to kill her. While she was quite calm and collected as she told him she needed his armband, she also seemed to look forward to figuring out how to extract it. We also never see that guard again...Hell hath no fury indeed!
The film opens with young Peter Quill witnessing the death of his mother in a hospital. As soon as she flatlines, his clearly distraught grandfather hurries him out of the room and quickly asks him to please wait right there. Peter runs outside, and is then abducted by Yondu. Earth is never revisited in the movie, which means that we never find out how Peter's grandparents react to suddenly discovering that their six year-old grandson has gone missing (and of course he's not going to be found) just after the already traumatic death of their daughter. Consider also how Peter's grandfather might feel incredible guilt for being the one who shooed Peter out of the room, never to see him again. And consider that, as his grandfather was likely in his 50s or 60s during the prologue, he's likely dead by the time of the movie's present setting and took that guilt all the way to the grave.
It turns out Yondu and his men were specifically hired to fetch young Peter for his father. Imagine if Peter had stayed at the hospital with his family, only to have a bunch of ill-tempered space pirates burst in and kidnap him. It's unlikely his family would have let Peter go without a fight, and it's even more unlikely that Yondu and his men would have had the patience to explain why they wanted Peter and would have just murdered them if they resisted. Chances are Peter inadvertently saved his family and dodged a very traumatic bulletnote Or floating arrow by leaving the hospital.
Peter's mother dies in the film's opening of a disease which, given her lack of hair, is heavily implied to be cancer. Years before, she somehow conceived a child with some ancient alien being even the Nova Corps don't understand. It is entirely possible that that is how she contracted the cancer in the first place. Who knows how much radiation a celestial being like Peter's father emits. Likewise, carrying a half-alien baby inside her body for the duration of a pregnancy could have jumpstarted Meredith Quill's cancer as well.
Considering Yondu's timing in snatching up young Peter so soon after his mom passed, along with the fact that she told her family that Peter's father would come and get him soon, it seems likely that she and her alien lover both knew that having a child together would shorten her lifespan in some way. And judging by how well things were timed, Peter's father probably knew exactly how long she had left, and thus knew when to tell Yondu to start heading for Earth.
Just take a minute to think of The Collector for a moment. He seems like an Affably Evil old kook, but he essentially IMPRISONS and ENSLAVES living beings for his "collection", no one is really safe from his clutches and its likely that he has impressive powers to make him above the law or even worse, no one really can or wants to stop him.
Speaking of the Collector, how many innocent people he enslaved died during the explosion on Knowhere? How many of the slaves that died considered it a release?
Another scary thing about the Collector... Let's not forget that he already possesses the Aether. Just how close did Ronan come to having two Infinity Stones in his possession?
The fact that those metal bits on his back are likely exposed bits of his skeletal structure. Though, while we're on the subject, those metal implants on his chest aren't as pronounced as the ones on his back, but they're a bit oddly placed to have any real function, so it's anyone's guess what they are or what they're for. They might be external ports to keep artificial organs charged and running, but... who knows?
The "Rap sheet" scene indicates that Rocket is from Keystone, like in the comic books, and lists some of his old associates, but given the origin for Rocket suggested in the film, this raises the question of what exactly is happening on Keystone, and how many other "test subjects" there might be. Given his designation, at least 89. It makes his impassioned speech to Drax a little more horrific, because just how many dead people does Rocket have to be in a position where he considers himself to be the "only thing like him."
Rocket's initial reaction to The Collector's... collection is the first time he is shown to be honestly uncomfortable with something (though he quickly brushes it aside in favor of his usual brusque demeanor)- given that he'd just had a drunken rant about his origins, it's horrifying in retrospect that he's seeing sentient beings being held in cages and treated like objects when he, himself, has probably been in a similar position.
The fact that Xandar and the Nova corp would apparently not only run a prison as horrible as the Kyln, but would send people there with no apparent legal proses. Granted, Qull, Gamora, Rocket and Groot are all wanted for multiple awful crimes, and may have already been tried but absconded (Rocket) or might have been tried in absenta (Gamora), but the fact that the Big Good civilisation in the galaxy has a penal system that seems to be worse than most developed nations on earth does not bode well.
Quill finds the orb in one of the very first scenes of the film, and since then drops it on the ground and throws it up and catches it again - several times - before finding out that it contains a goddamn Infinity Stone.