Continuity mistake: In the scene towards the end of the film where we see Slade's body fall, it falls onto a submerged rock just below the surface of the water and there is a splash of water. In the next shot Tarzan looks down from the cliff above and Slade's body is on a large dry rock, a little distant from where the body originally fell.
Continuity mistake: When the men first enter the spaceship, one of the windows shows an afternoon sky and the one next to it shows a nighttime sky. (01:11:20)
Continuity mistake: Ben-Hur places his crown on a table when he visits the fallen Messala, but upon returning the table and crown are gone. (00:36:35)
Continuity mistake: When in James Mason's house in South Dakota, Cary Grant writes a message to Eva Marie Saint on a matchbook from which several matches are missing. When Ms. Saint subsequently reads the message the matchbook is full.