When Peggy is doing the crossword puzzle on the train, Harold tells her he has the solution for clue number "19 Vertical". The puzzle is shown twice in close-up, and there is no "19 Vertical" - clue 19 is horizontal only.
The glass partition between Harold and the driver disappears and reappears.
Peggy is shown in close-up doing a crossword puzzle with a pencil in her right hand. The more distant shot immediately following shows her holding the pencil in her left hand.
Right after the coach states that he's going to teach his team to tackle if it takes all night, Speedy is shown being tackled with his shadow stretching out behind him. When he stands up in the next shot, he is lit from behind, with his shadow in front of him.
When Harold is "sitting" at the table while getting his pants fixed, the girl he is sitting with would clearly see that Harold isn't sitting at all and his legs disappear behind the curtain.
When Harold and Peggy are taking turns suggesting possible solutions to 19 Vertical, the words are not all of the same length and could therefore not all be possible solutions.