Other mistake: When Peter is dancing to his musical number on top of the table, his head continually shrinks until the end of the shot, where his head is around a third of what it was originally.
Other mistake: After Brian says Chris is tweaked and Chris says maybe the toad is Meg's, the bubbles in the aquarium stop moving.
Answer: Mort is Jewish, and Walt Disney was said to be antisemitic. So it would make sense in a Disney universe all the inhabitants would share his supposed beliefs.
MasterOfAll