Continuity mistake: At the end of the scene with the ex-leper you see Brian's mother open the door to their house twice; first in the background of a wide shot, then in a closer shot. (00:15:25)
Visible crew/equipment: When Brian's mother tells him that his father was a Roman, you can see the shadow of the boom mic on the wall behind Brian. (00:17:20)
Continuity mistake: When Stan says he wants to be a woman at the coliseum, he is facing to his left. In the following shot, he is facing down and to the right. (00:19:25)
Continuity mistake: During an early scene, the People's Front of Judea are conversing while Brian is selling food. The man to the right of Reg has no tear in his shirt collar at the beginning of the scene. Once Brian approaches them his shirt collar has a significant tear that wasn't there before. (00:21:20)
Continuity mistake: After Brian is caught by the alien spacecraft, his yamulka is in front of his hairline. But, once the camera pulls away to show the aliens his yamulka is placed very far back on his head. (00:43:09)
Visible crew/equipment: When the spaceship is being attacked, the alien bumps up a bit, and if you look closely you can see a face under the right hand alien. (00:43:28)
Revealing mistake: When Brian falls from the tower and knocks the prophet, we can see Graham Chapman (Brian) is actually hanging on a bar. (00:52:15)
Visible crew/equipment: After Brian had his speech and the people pursue him asking him to complete his sentence, there is a frontal shot of Brian and the people where they push a blind man to the ground. You can see the shadow of the camera man on the crowd as they are walking. (00:55:15)
Revealing mistake: When the blind man is telling Brian he can see again and falls down in the pit, you can see the white mattress that he lands on. (01:01:10)
Continuity mistake: In the balcony scene, the Gourd Follower woman is in the foreground in shots from the window, but long shots show only the man behind her. (01:07:00)
Continuity mistake: At the crucifixion, the soldier says, "Let's settle this" with his arms raised. In the following shot on his front, his hands are on his hips. (01:23:35)
Audio problem: When the leader of the Suicide Squad introduces himself and his team to Brian, we can see his original lines have been over-dubbed on the post-production. (01:27:55)
Visible crew/equipment: A man appears from behind the second to last cross in a black waistcoat/jacket and white pants, the van he came in (presumably) is there too, and appears again later in the song, only for a short few seconds though. (01:30:20)
Visible crew/equipment: In the last scene while Brian and the others are singing you can see a tourist walking in the background. (01:30:30)
Other mistake: When Brian is being chased by people who believe he is the Messiah, Brian loses a sandal. They all think it's a sign and run after him with one sandal in their hand. Thing is, when you see them, thay all have both sandals on their feet, yet most of them are holding a sandal. Where did they all get their third sandal from?
Continuity mistake: Pilate is making his guards laugh by telling them about Biggus Dickus' wife Incontinentia Buttocks. Brian crawls away, while Pilate rushes up his steps in a wide shot of the room. But then the camera cuts to a close-up of Brian, and he crawls away again.
Visible crew/equipment: You can clearly see overhead wiring during the manger scene near the beginning.
Continuity mistake: The cross carried to the crucifixion scene by the Saintly Passer-by looks nothing like the one they crucify him on. The cross bar is a narrow pole, and the upright is much smaller than the one he ends up on. They do not crucify him on a different cross - he is roughly pushed down on the flimsy prop cross he carried, then instantly is hauled upright on a sturdy one.
Factual error: There were no gourds in Ancient Judea, of that type. The 'gourd' mentioned in the Bible refers to a colocynth plant, which yields only a small fruit, 5 - 10cm diameter. The gourd in the film is from a pumpkin, and not from a watermelon, as others have suggested. Pumpkins originated in the Americas, and there weren't any in the rest of the world before Columbus.
Suggested correction: This is a movie where Brian falls inside a flying UFO with alien pilots. I seriously doubt that the filmmakers had any intention whatsoever to be historically accurate.
Regardless of the random UFO scene, this is still a factual mistake. It doesn't matter if a film maker sets out to intentionally make a historically accurate film or not. There's nothing to suggest this film was set in an alternate past or that it was a sight gag as if it was a Mel Brook's film.
Continuity mistake: When Mandy and Brian are walking home after the stoning, Mandy tells Brian he needs to get a job. But a few minutes later, when the ex leper is bartering with them for a donation, Mandy says that one of the prices he's asking for is more than what Brian makes in a month.
Suggested correction: She was lying to him to get him to go away.
Suggested correction: He's got a job - selling otter's noses and other delicacies in the arena during gladiatorial meets.