Christopher Lee's mummy walk isn't entirely acting. Besides the injuries to his back and shoulder noted below, he also injured his knees and shins while doing scenes in the studio-tank "swamp". He couldn't see where the various pipes and fittings under the swampy water were.
Hammer Films had already done remakes of Universal's classics Frankenstein (1931) and Dracula (1931) (Frankenstein s'est échappé (1957) and Le Cauchemar de Dracula (1958), respectively). This was the first film made after Hammer reached an official agreement with Universal Pictures (then Universal International) allowing them to do remakes of their classic horror films. In this film, for example, the agreement with Universal International allowed them to use the name Kharis.
A door through which Sir Christopher Lee must crash was accidentally bolted by a grip before the scene was shot. Lee's shoulder was dislocated when he broke down the door, but the shot remains in the movie.
The squibs used when Peter Cushing shot Christopher Lee left burn marks for a few weeks. Lee also threw his back out carrying Yvonne Furneaux.
Director of photography Jack Asher wanted to create the impression that the tomb had not been opened in thousands of years. So he had a crew member climb into the catwalks above the set to spray the air with water before each scene. As the water particles descended, they would take all the smoke and dust with them, leaving the air completely clear.