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Nightmare Fuel: Planes
The entire sequence of Dusty crash-landing into the ocean. Had he never gotten rescued, he would've drowned.
The war scenes involving "Skipper" seemed a little dark for a kids movie, especially when you start thinking about these characters going to war with each other. Also several sentient planes get shot out of the sky, by what I assume were sentient battleships. Once you remember these aren't just vehicles, that scene becomes almost as brutal as Omaha Beach.
Disney is known for slipping in very dark moments into their movies and franchises, but what that one scene did was add an entirely new layer onto the Cars universe. While the Cars franchise sounds like a gimmick, the flashback adds a new layer to the world by telling us that, yes, wars even happen in this world. So while Cars 2 and Planes might be cash-ins on the original, they also do things in these movies that further builds upon the world of Cars.
And not only do wars happen, but the warplanes and ships (and presumably tanks) are alive just like all the other machines. They are built for war, and war is all they know. After the war, Skipper had nothing to live for, because he was a warrior with no war to fight.
Sarge from the original Cars would also fit this, though he was able to open his surplus store once he retired (maybe he was in Supply when he was active military?)
The scene where Dusty almost crashes into a train.