Planet 51 (2009)

Revealing mistake: After Chuck steps on the toy duck, he looks up to see the alien family and their house behind them. However, there is no reflection of this on his visor, just an empty field and the trees beyond.

MrNelg

Continuity mistake: As Chuck first arrives on Planet 51 he takes a few steps. The ground in front of him is clear. As he plants his flag down he steps on a duck which wasn't there before.

Low Cow

Continuity mistake: When Eckle's mother leaves the parking slot (after pick up Ekle from theater) there is a lamp pole that goes down (thanks to that alien dog). In next frame the lamp pole is instantly fixed.

bacalhau_cnatas

Trivia: When the Hazmat team are dropping objects into the containment pod, they drop in a magazine called "G.A." On the cover are a number of titles regarding the making of the movie, including one that reads, "G.A.'s Lifestyle Advice: Go to the Movies to see Planet 51."

MrNelg

Lem: Lem. Llllleeeeeemmmmmm.
Charles Baker: Either your name is Lem, or you want to mate with me. Houston, we have a little problem.