When Bourdette confronts Mr Houston, he pulls the sheet of paper out of the typewriter, and crumples it up - but when Mr Merriner picks it up to read aloud what Mr Houston had typed, the piece of paper is in pristine condition.
When Raymond and Mr. Marriner are looking at the "wax" figure of Armstrong, you can see the actor playing Armstrong move slightly and almost blinking.
At the end when the chamber is opened, the attendant tells Mr Marriner that he hasn't heard a sound from Houston all night. However at one point Houston panicked and was banging on the door.
The tour guide who sold Barry Nelson's character a tour book raised her head from looking down at the coins in her hand twice in rapid succession starting at 2:20.