Continuity mistake: Niles is showing Marty how he can kick box and he accidentally kicks Daphne. The tray she is covering flies up in the air, and the snack food ends up on the footstool and the floor. There is also an empty basket in front of the footstool. Niles goes to the kitchen to get ice for her wrist; when he returns most of the snack food and the basket have disappeared.
Audio problem: After Mary says "Except I bet you didn't walk through a metal detector to get to class", Frasier in that shot does not move his mouth in line with the dialog that he speaks, but instead appears to be laughing. Additionally in the next shot, although his mouth now matches his dialog, he is half way out of his seat despite being sat in it in the previous shot.