Revealing mistake: About half an hour into the movie, when Frank is in the tank, he plows into a supposedly concrete zoo wall, which wobbles. Also, the wall splinters where it meets the sidewalk, revealing that the "wall" is actually a wood prop, and a flimsy one at that. Five seconds later, when people and animals are shown running out, the same wall is shown with a different shaped hole and pieces of concrete lying around it. Apparently the concrete pieces aren't too real either, as the camel kicks one around as easy as if it were made of foam.
Revealing mistake: When Frank drops his helmet into the machinery below him, cogwheels start flying. Then it cuts to a closeup of Frank and a cogwheel suddenly strikes the roof right in front of him. However it is obvious that the cogwheel comes through the roof from above and not from the machinery below.