Rover is programed to find alien lifeforms, so what does he do when he first meets one sitting on one of his "precious" rocks? ...He squished it! Makes you feel bad for the little alien.
This is a planet full of aliens and you sent us pictures of ROCKS? Bad dog!
Rover in general.
When Chuck and Lem do their dance number for the "Humaniacs" fans.
The inhabitants of Planet 51 have gone through a great deal of preparation to hold the "alien", so when the general and Chuck have their first conversation, the former goes into great detail into how any attempts to control any one of the soldiers will be countered by another soldier's orders to shoot the compromised soldier. He goes into such great detail that it turns out just about every soldier has a good half-dozen different potential targets, not counting the soldier who only has orders to graze the last of his targets and the soldier in the back who has orders to electrocute the floor. Naturally, the soldiers get confused and the whole thing goes to Hell, prompting the mass electrocution of the room (save Chuck - rubber boots maybe?), and the general gets a mixed in Awesome Moment when he not only endures the electrocution, he starts ordering his troops to calm down - at the top of his voice.
Chuck trying to convince the Professor he doesn't want his brain.
Chuck: I spent 4 years at a party school. It's mush!