Continuity mistake: When Don Knotts is in the old Simmons mansion, he falls down a chute of some kind. If you watch closely you will see the stunt person looks nothing like Don Knotts. It is a younger man with very straight hair.
Continuity mistake: When Peter O'Toole is locked in the closet at the museum, he puts a rope through the keyhole and uses a hook to pull it under the door. In the first shot, from outside the closet, the end of the rope is to the right. In the next shot, from inside the closet, the end of the rope slides under the door to the left. (01:22:30)
Audio problem: When Alfie and the other mechanic are at the shed, the mechanic asks, "Are you getting serious with her?" and his mouth is not in sync.
Factual error: Cary Grant arrives at his Tokyo hotel two days early, and no rooms are available. He goes to his embassy, which, according to the sign on the gate is the "British Embassy". In reality, the sign would say, "Embassy of the United Kingdom of Great Britain and Northern Ireland".
Continuity mistake: As George says "That you people are rearranging my genes so that everyone will be like everyone else" he puts his left arm around Nick. His hand, though is on the back of the sofa. Instantly in the next shot, however his left hand is now on Nick's left shoulder.
Continuity mistake: When Mama does the fateful reveal, in the close-ups she keeps the coat open, hands on the lapel, while in the wider angle she has it closed, hands in pocket. (01:45:25)
Factual error: The uniforms worn by the engineering force are from the wrong era. Prior to 1941 the left arm rates had the head of the eagle pointing to the wearer's rear. Steve McQueen and the rest of the Engineering force rate eagle head is pointing forward, which is from WW2.