After Quincy falls onto the cake he gets up to chase after Nicky. The back of his shirt is completely clean with no sign of any frosting from the cake.
Toward the end of the film when Quincy is running alongside the train yelling at Nicky the passengers in the neighboring cabin alternate between an older man and a younger man.
When Quincy shows his work to Evan at his house, his sideburns switch from connected as a goatee to regular sideburns from shot to shot.
When Quincy goes to Nicky's house to find her after he discovers that his cousin is marrying Rita. When he has the conversation with Amy her hair changes position between shots.
When Evan tells Quincy that Nicky has cut her hair, Quincy sits back in his seat with his right hand over his mouth, but in the next shot, he has his left hand over his mouth.