The Methods that the scientific community used to discredit Charles Muntz's Fossils have been themselves discredited over time as grossly inaccurate. In other words, Muntz was right when he said the skeleton wasn't a fake. It only makes his turn into madness that much worse.
Kevin's tendency to swallow inedible objects comes off as typical dumb, goofy cartoon bird at first. Later, you realize that Kevin's actually looking for food to store in her crop for her chicks, which can't leave the labyrinth. She's testing any new object she finds for edibility, as food would be fairly scarce on the plateau, and learns very quickly which things are edible and which are not.
In the first few minutes when Russell is telling Carl about the Wilderness Explorer badges, he mentions that the ceremony for the promotion to Senior explorer involves all the dads attending. That's why he's so dedicated to getting all the badges: he wants to see his dad. This even makes the ending a bit heartbreaking: Russell's dad doesn't bother showing up to an event that specifically calls fathers to participate in. It's nice that Russell has Carl in his life at that point, but what a douchebag Russell's father must be!
The first or second time that you watch the movie, you wonder how Carl, obviously an older man, would have survived without running water, electricity, or an unlimited food supply. But then you realize that Carl never wanted to live in Paradise Falls. He wanted to die there.
At the end, Carl, Russell and Dug are playing a game in which they point out the colours of cars. Dug shouts "grey one!". At first, you think nothing of it. Then you realize: Dogs are colourblind.
Can a joke based on scientific inaccuracy be labeled as Brilliance? Dogs don't see in black and white, they're red-green colorblind. Dug would be able to see blue, yellow, and violet in addition to greys, white, and black.
Then it was a red one!
Dogs interpret red as yellow. It was more likely actually gray.
This troper thought he was referring to the Spirit of Adventure when he said that. It was parked right next to them.
It's actually a different kind of brilliance - Generally when people play these kinds of games in movies they talk about cars like red, blue, or yellow cars. Colorful cars. But the most common colors for cars are white, silver, black, and grey. If you assume silver and grey would both be considered 'grey' by the average person then grey cars are the most common car in the world. Of course he'd see a grey one!
Muntz has never tried using chocolate as a lure for Kevin. Why? Because he has a LOT of dogs and dogs and chocolate don't mix well.
On a related note, it makes sense that Kevin is fond of chocolate. Living in South America, one of the plants available for Kevin to eat would be cocoa seeds.
That does raise the question of why he never tried that in all those years.
He never went outside. He only sent out seeker dogs to find the bird, and the dogs are trained to place traps as shown with them able to tie up Russell. The only time he's outside is when he's grabbing the bird and setting the house on fire. You'll even notice that he stays in the entrance of his domain before coming out in broad daylight when he meets Russell and Carl. He probably didn't do any other research with the landscape other than to draw it out as a map from his blimp.
When Carl goes down in the stair lift, the music is la "Habanera" from Carmen, which is about how love is unpredictable. Some of the lyrics are "if you don't love me, I love you, but if I love you, beware". Carl doesn't like Russell or Dug but ends up loving them both; and he loves Muntz, who will try to kill him.
It's been said that insanity is doing the same thing again and again and expecting a different outcome. Make of that what you will.
When Russel mentions Phyllis, Carl asks if he calls his mom Phyllis, to which Russel, slightly surprised, replies, "Phyllis is not my mom." Of course he would be surprised, when they arrived to Paradise Falls, Carl said he wanted to play a game about being quiet and Russel says his mom likes that game too, using the word mom!
Some have wondered why Carl would turn against Muntz, since he and Ellie were such big fans, and Carl treasured anything related to Ellie's memory. But the both met each other because of their common admiration of Muntz — that was only the beginning. Their marriage and life was about each other, not Muntz or worship thereof.
When Muntz was showing off his fossil collection, he made the statement that he "kept the best for [himself]". Syndrome said the same thing of his gadgetry shortly after confronting Mr. Incredible. That line was probably foreshadowing of Muntz's true nature.
When they first reach the jungle, Rusell has to go to the bathroom and just does it there in the dirt. We never see him wash his hands after that, and then just right away he touches and eats the chocolate he gives to Kevin.
Uh, as someone who has gone camping, there are ways to do one's business without touching a lot of gross stuff. It's not that horrific. And we don't see Russel washing his hands for the entire trek. Not that he could, since there's no running water or soap. I'm sure he's touched worse things than some dirt and his own waste all while feeding bits of that chocolate bar to Kevin.
Maybe he's got a bottle of hand-sanitizer in his pack.
The pilot caps Muntz keeps as souvenirs of the "trespassers" he dealt with look identical to the one Carl owned as a child and he owned that cap because he was a fan of Muntz. In other words, young explorers came to Paradise Falls to see if they could find Muntz and his bird, and got killed by their childhood hero.
Along a similar line, one of the dogs had said "I like you temporarily." This takes on much darker tones when you realise how temporary that "like" could be... and that the dogs knew it, too, because it had happened before.
In the short "Dug's Special Mission" we find out Dug's birthday wish was for a new master. This raises the question: just what the hell did Muntz do to poor Dug that led him to make that wish?!
More then likely? Neglect. Muntz has a lot of dogs, and Dug most definitely isn't the favorite.
Here in Italy we have a saying: "Even a dog wants a pat". Being a dog lover, I know how true this is.
Here's an even darker theory: Dug's original owner was one of the explorers who was killed by Muntz.
That would actually make a lot of sense, after all all the other dogs of Muntz are dobermans, rottweilers and bulldog or a mixed breed of either, only Dug is a golden retriever...
When they fly back home, Carl and Rusell are wearing aviation hats. Cool eh? Wait.... where did they get the hats from? Yeah, sure take the dead people's hats Carl.
Maybe Muntz has spares/extras?
When Muntz shows Carl the hats in question, he holds up one, and says "A man taking his house to Paradise Falls"... even though Muntz has yet to kill Carl. I highly doubt all of those helmets belong to fallen explorers.
So, the main fan theory is that Carl was planning to take his house to Paradise Falls and die peacefully so he could join Ellie. So, what would have happened to Russell if he had gotten to live out that plan?
He would have sent him home, like he tried to do at first when they got to South America. Carl is not a monster.
Yeah, but how? They were in the middle of a South American jungle. There's no sign of civilization anywhere, and Russell's GPS went flying out of the window at the beginning of their journey, there's no way to contact anyone. And I doubt Carl has enough balloons left to make a return trip for Russell.
There seems to be only one bird like Kevin. Did Muntz kill Kevins mate?