While Gil is disguised as Santa, he is paler in some shots than in others.
Lisa has a note from Gil saying "Thanks for the bologna." However, at this point in the story, Lisa is established as a vegetarian, and would not have packed bologna.
When the guy in the Grinch costume is standing outside wielding a knife, his hand is pressed against the window, yet he is making a stabbing action in between the glass and his other hand.