Factual error: The family stays briefly in a British apartment, however the plug sockets displayed are US standard, not UK.
Factual error: In the very beginning of Perfect Castaway, when Peter is talking to his workers and telling them he's going to have to "put them down", he pulls out a shotgun and four shells. He puts two shells in each barrel, but then continues to shoot 5 times when they jump in the water. First of all the shotgun is a double-barreled, break action type shotgun, so Peter should only have been able to put two shells in it. Second of all, even if he could put two shells in each barrel, he would only be able to fire it four times.
Fast Times at Buddy Cianci Jr. High - S4-E2
Factual error: At the end of Peter's trombone solo, he holds out his last note. While holding the note, he moves the slide with no change to the note whatsoever. Since the pitch of the trombone is controlled by the slide, it would be impossible for Peter to move the slide as much as he does without changing the pitch he's playing. (00:02:00)
Factual error: When Stewie is playing Simon Says, the sequence Stewie plays is different than the one that the Simon Says played. If he played it wrong, there should have been a sound from the Simon Says indicating that Stewie played it wrong.
Factual error: Quagmire spikes Brooks drink. She takes a drink and immediately passes out. The pill didn't even dissolve let alone get in her system long enough for her to pass out.
Factual error: When Lois, Meg, and Chris go to the stage show on the West End, "theater" is spelled with the Americanism "-er" instead of the UK spelling "-re."