Continuity mistake: When Emily falls off the roof, one shot shows her falling with her back first and her legs together. Then the shot changes to her mom, and back to her, at which point her legs are further apart, she is angled more headfirst, and is still at the same height.
Continuity mistake: In the shot of everyone chanting, "disco ball!" Hermey is seen in the background, but two shots later, Hermey has disappeared. (00:19:00)