Grease (1978)

Continuity mistake: The scene where Sandy and Danny are eating together, then the rest of the gang comes, Sonny walks Marty home. Right after the two leave, Sonny come up behind Frenchie, like he was in the bathroom or at the jukebox. Wasn't he walking Marty home?

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.

Continuity mistake: When Sandy tells Danny that he is a fake at the pep rally, we see Rizzo, Frenchie, Jan and Marty standing behind her in a line. In the next shot, Jan is standing directly behind Rizzo.

Continuity mistake: When Tom and Sandy are eating an ice-cream sundae at the ice-cream parlour, Tom gives Sandy some money for the jukebox. After Sandy gets up from her chair, Tom then sits back in his chair and he is looking forward, but in the next shot he is looking over his shoulder at Sandy.

Continuity mistake: When Sandy and Tom are eating an ice-cream sundae at the Frosty Palace, Tom takes a piece of ice-cream and puts the spoon in his mouth, but in the next shot he has his spoon back in the sundae glass.

Continuity mistake: After the race in the LA River, the black losing car is left in the middle of the river. When Sandy is talking to Frenchie, the car has been removed from the river. And finally, it's back in the water again.