The desert scene in the prologue was clearly shot in a quarry of some sort. Amusingly enough, thousands of years later, the same quarry represented the same desert with no change in the piles of sand. An amazing coincidence since the area had just been struck by a massive sandstorm.
As she walks through the hotel lobby, Claire is wearing red lipstick; when she is stopped by the fortuneteller at the door, she has on pink lipstick; when she reaches her destination, she appears to have no lipstick at all.
Prior to John Phillips' head being smashed against the wall, the fake blood is there before his head hits the stone.
In the climatic struggle, the police officer shoots the mummy in the back twice. In the next following shot, the bullet holes are gone, but back again in all subsequent shots.
When Stanley Preston's press conference in front of the mummy ends, all the reporters disperse. The film then cuts to a close-up of the mummy, in which several of the reporters's head's are visible on the bottom of the screen.
The mummy starts a fire in the photography studio; the curtains on the other side of the room start burning by themselves a moment later.
At the start, Prem has just laid his master's body to rest and walks outside into the desert. There is a low evening 'sun' and his shadow is cast on the faraway mountains and sky revealing them as a backdrop only 4 or 5 feet away.
As Paul Preston is being chased by the mummy during the film's climax, the zipper seam on the back of the mummy's costume is clearly visible.
After the mummy is shot, the camera focuses tight on his back as he advances. The mummy gets far enough away to reveal the actor is not wearing his headpiece.
During the press conference in front of the mummy, the arm of the mummy moves in time with the actor's breath.
During the prologue, it's told and shown to the viewer(s) that only Prem, Kah-To-Bey, and two slaves have survived out of the original party that ventured into the desert. Then Kah-To-Bey dies. How do three men carve an elaborate, subterranean tomb for him in the middle of nowhere, with no natural resources, that would've taken more than just the rest of their lives? There's no way the current Pharoah would help; he wanted him dead in the first place. Oops.