When Troy is hit in the head with the cake, the first strike is in a totally different place than seen in the next shot.
In the opening scene there are 3 high school kids seated behind Britta. Before they talk to Jeff and Britta, the boy sitting next to the girl is clearly leaning to his left to be in the shot, and he's looking forward and conversing with nobody across the table from him.
When Shirley pants-es the high school girl near the end of the episode, her pants are already conveniently unbuttoned.