Continuity mistake: The flashback is set in 1993, but all the characters look the way they did three years later. Most noticeably, Frasier's hair is short and not long and wavy like in the first season. Daphne's appearance has changed quite a bit too.
Continuity mistake: Daphne is on the phone with her mother and has a dust rag in her hand. She holds out the phone towards Frasier and when the shot goes back to her, the rag is all bunched up in her hand - it has been loose before. There was no time for her to change it.
Continuity mistake: Niles and Frasier are at Marty's old apartment and Niles sits down on the couch. Eddie is sitting next to him, staring. During this scene, the shots of Eddie show him moving from fairly close to Niles, to about 10 inches away, and then back again. He has no time to change position naturally.