Other mistake: In the scene when Professor Kelp sticks his arm in the punch bowl the fruit juice stains his white jacket sleeve red. When he goes to his laboratory to make more formula to become Buddy Love, his white shirt sleeve underneath his stained white jacket sleeve is still white. It is hard to believe his jacket sleeve would stain and not his shirt sleeve as well.
Continuity mistake: In the first scene with Stella and Buddy Love at the Purple Pit, Stella's eye shadow is bright blue and extends above her eyebrows. When the scene moves to the hill above the city, her eye shadow switches between nonexistent and a light green. (00:46:00 - 00:50:45)
Professor Julius Kelp: Well, just don't do something, sit there.
Trivia: While the principal of the school is going through the list of everyone performing at the prom, he mentions a comedy duo, and says "Oh, I thought they split up." A wry reference to the earlier break up of Martin & Lewis.