When Ed hits Fleischman with the tomato the stain on Fleischman's shirt changes between shots.
(At around 36 minutes) As Marilyn prepares to enter the doctor's office from the street, she has a star-shaped barrette at the back of her head. When she enters the waiting room, the barrette is gone, but when she enters Joel's private office moments later, the barrette has returned.
Based on time elapsing and seasons changing in the show, there's been two springs for example, Joel is wrong when he has says there's 3 years, 9 months, 1 week and 7 hours left of his Cicily sentence. It's more like 2 years 9 months.