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)
Continuity mistake: When the senior guard speaks to "his Excellency" and decides to turn off the alarm, he reaches to his pocket to produce the key. However, in the moments when the telephone rings and he walks to the phone, the key was left in the alarm vault door.
Continuity mistake: When Audrey Hepburn, posing as a cleaning woman, is scrubbing the museum and attempting to escape to the guard room, she notices the large engagement ring and removes it from her finger. In the very next scene, where she is scrubbing the pillar and holding the bucket, the ring is still on her finger. The ring catches a flashing reflection as the camera pans away.