When Imhotep is talking to Alex on the train with the mask on you can see the actors neck and teeth not the decayed teeth or neck. The teeth you must look good for. But when he is bent down to talk to Alex you can see the actors neck (skin) very well. When Alex pulls the mask off, you see the decayed teeth and decayed neck of Imhotep. Should have done a better job of covering up the actors real teeth and neck.