Revealing mistake: When the debris covers the trapdoor, some debris from behind it overlaps the debris on it. (00:09:13)
Revealing mistake: When the ceiling begins to collapse, some of the debris freezes in midair. (00:08:52)
Revealing mistake: When the camera scrolls to Grunt (in the scene where the gang are locked up in a cell, being watched a strong, non-human security guard named Grunt), he appears out of thin air. The animators might have had some trouble putting him into the scrolling shot. (00:11:15)