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.
Other mistake: When they are flying the dirigible through the night you can cleary see that there is a repeated pattern in the stars.
Answer: He says that it means 'it's as hot as hell'.