Revealing mistake: Just after Mr. Creosote explodes and all of the guests are vomiting, there is one male guest third from the front that is puking. Though his hand is up near his mouth, it is clear that the puke actually comes from his hand rather than his mouth, revealing that he is holding something that produces the fake vomit.
Revealing mistake: In the organ donor scene, when the guy takes out the liver, you see him turn to his left to pick it up, so you can tell he didn't take it out of the guy.
Revealing mistake: During the sperm song in the "Miracle of Birth part II" there is one shot where the kids are dancing down the street. Watch the girl at the front on the left. She hesitates and then runs to catch up to the front line. Then when they go round the corner, she has to be moved along by the other kids as she stops to stare at the camera.
Revealing mistake: Near the beginning of the 'Crimson Permanent Assurance' sketch one of the guys running out in panic quite badly clamps his fingers in the door yet it doesn't appear he really hurt himself much.
Revealing mistake: When Mr. Creosote pukes on the menu, the puke comes out before his mouth opens.
Revealing mistake: When the Indian servant is stabbed in the back by one of the Zulu warriors, we can see that he is wearing something under his jacket to enable the spear to stick to him. (00:51:15)
Answer: Graham Chapman.
Xofer