Continuity mistake: After they've kidnapped Alex on Tower bridge, they raise it to aid their getaway. The next shot is of Imhotep and Anck-Su-Namun standing looking over the city from a balcony - you can see the bridge, and it's lowered. You might think that that shot takes place a while afterwards, and the bridge has since been lowered, but then it goes back to Rick and Evie, and you can both see and hear the bridge lowering back into place.
Continuity mistake: After the cast makes a getaway on the double decker bus, the little kid jumps on John's back and says, "Nice job." When the shot cuts, he is still there. In the next shot, the bus is pulling over to the side of the road and the boy is not on John's back anymore.
Continuity mistake: Imhotep is using water to chase after Izzy's airship. The water ends up drenching the entire ship. In the next scene, Rick and Evelyn have dry hair.
Continuity mistake: When Imhotep's holding onto the edge of the floor above the Underworld he's using his right arm to do so. A shot of Rick and Evelyn backing up then he's shown holding on with his left arm.
Continuity mistake: When one of the men in red is looking at the pygmy in the tree, the pygmy's face is looking up slightly (right before the first man is attacked) and has his mouth relatively open. But, right before it wakes up, its head is slightly down, and the mouth is less open than it was before.
Continuity mistake: When Rick turns around finds Alex, Alex falls back and his hat falls off and rolls back a few inches, resting a few inches from the top of his head. However, after Rick says his name, it cuts back to Alex and the hat is practically under his head, almost behind his back.
Continuity mistake: When Rick jumps off the dirigible to save Evy after she has the visions, he is holding onto the railing. However, in the next shot, Jonathan and Ardeth are the ones holding onto Rick.
Continuity mistake: During the scene when Imhotep controls the water and raises it up he starts with straight arms, as shown in the shot with his back facing the camera. However in the next several shots showing him from the front he has bent arms, then straight arms from the back again.
Continuity mistake: When Imhotep is talking to Alex O'Connell on the train through the black mask, his teeth are perfectly white and straight. A few seconds later, when Imhotep takes the mask off to show Alex, his teeth are like the mummy's - brown, green, jagged, and decayed.
Answer: He says that it means 'it's as hot as hell'.