Continuity mistake: During the race at Thunder Road, look at the length of the wheel cutters - they keep changing length throughout the whole race. Plus we only see one come off, but before the crash the two Westside ones are missing.
Continuity mistake: When Danny and Sandy enter the sports hall for the National Dance Off, there are four people behind them sitting on the spectator benches, but when Doody and Frenchy enter the hall in the next shot, the people have disappeared and there is now a woman in a pink dress behind the benches.
Continuity mistake: When Jan is mimicking the Ipana squirrel on TV, she put her hand up to her mouth when she is singing, 'Brush-a Brush-a Brush-a', and pretending to brush her teeth. In the second half of the song, however, after the second line; 'New Ipana toothpaste', she has both her arms pointing in front of her making a 45 degree angle with her body, and her neck straight but in the next shot, which is at the beginning of the next line, 'Brush-a Brush-a Brush-a', she has one hand up to her mouth again and her head is pointed a little to the right. You might also notice that the time between those two lines is longer than it should be.