Plot hole: At closing time, Cliff, Norm and Woody spontaneously decide to go to Cliff's house. Sam then enters the bar after his date at Melville's. Later in the scene, Rebecca asks Sam about the 'Three Stooges', to which Sam sarcastically replies that they went to Cliff's house. But how could he possibly know that since he entered the scene after they had already left.
Revealing mistake: When Frasier comes into the chalet after skiing he doesn't show any of the visible effects after a hard day on the slopes. Meaning, his face isn't even flushed from the cold, his hair is perfectly combed after wearing a hat and there is not even a drop of snow on his boots.
Other mistake: Right after Sam tells Carla he will sleep with the next woman who walks through the door, in the background there is an "Extra" (blonde-haired woman seen in background between Sam and Carla) who starts to cross right then turns and crosses lefts then turns right and stops and looks confused as to where she is to cross. Obviously she was given directions of which way to cross and when, but forgot.
Continuity mistake: In the scene where Carla is sitting at a table in the bar, dressed as the new Madame LaCarla and is voicing her doubts about being the new Madame, you can see that Carla is only wearing ONE earring. (left one). In other scenes she is wearing both earrings.
Continuity mistake: When Sam tells everyone it's closing time, he asks Harry how he got into the bar whilst he is playing snooker. He replies and then places a white snooker ball two inches behind a blue ball. There is also a yellow ball about three inches to the right of the blue ball. In the next shot, the yellow ball has suddenly moved a foot away from the blue ball. The yellow ball returns to its original position three inches away from the blue ball in the next shot.
Continuity mistake: At the point Cliff is disputing the fact that he thought his answer was right, on the right-hand side you can see the woman player's, Agnes, score. It says $400. Then in the next shot it changes to $3300. Then in a little bit later it changes back to $400.
Continuity mistake: Just before they reveal the answers of Final Jeopardy, they take a wide shot, and Cliff's question (Who are 3 people who have never been in my kitchen) is already revealed. But when they take a tight shot and ask Cliff to reveal his question, it is covered up.