Continuity mistake: When Richie gets up from a table at Arnold's to meet with the Fonz in the men's room he's wearing jeans. When he enters the men's room he's wearing grey slacks. (00:07:50)
Visible crew/equipment: When Al, Fonzie, and Howard use "Gulper" in the diner's kitchen, it starts to throw salad all over. You can see the same hand twice in a short period throwing salad from the door window. (00:13:40)
Answer: When it was originally broadcast there was a different ending. A new ending was added when the show was rerun to set up the Mork and Mindy series.