Sleeping with the Enemy - S3-E6
Character mistake: Noel Shempsky (the supposed Star Trek Nerd) attributes the quote "The needs of the many outweigh the needs of the few or the one" to James T. Kirk, when it was Spock who said it. (00:03:50)
A Long Walk To Pittsburgh (2) - S4-E17
Character mistake: In this episode Cory says that Topanga gave him his first kiss at age 13, but their first kiss actually happened when they were 11, in the 6th grade. (Season 1 - Episode 7 Cory's Alternative Friends).
Character mistake: While driving in a taxi, Fran says McDLT was discontinued in 1994, but in fact it was three years earlier in 1991.
Cat on a Hot Steel Beam - S1-E60
Character mistake: As the fire truck darts out from a back alley, the sign on a nearby gift shop window reads "gift's" when it should be "gifts".
Character mistake: When Clark flies to see his parents for the first time, he is wearing a maroon shirt and jacket. When he lands at his parents farm he is still wearing his jacket and maroon shirt. In the next shot, he has taken his jacket off which now has a rip in the shoulder, as he enters the house his shirt is blue, and then in the following shot at the table having dinner his shirt is again maroon. (00:30:00 - 00:30:50)