When the boys are first outside Porky's and the Sheriff pulls up, a closeup of Porky's face is shown and his cigar is not in his mouth. In the next shot, Porky is in the background and is shown taking his cigar out of his mouth.
When Mickey came back to the high school from Porky's after he got his big whupping from him, nobody who looked like any of Porky's goons was behind him when he crashed into the table with the record player and records, hinting that somehow after such a brutal beating he was able to drive all the way back from Porky's and run to the table before collapsing.
After Tommy comes out of the bedroom at Cherry Forever's house acting as if he was stabbed to death, the door closes over, but not all the way. However, almost immediately after this, the door is closed fully when John Conklin busts through it.