I watched this the other night on DVD, and noticed some high-pitched noises during some of the more tense scenes. Also, during several of these moments my dog would start barking and run around the house just out of the blue. She almost never does this, and I'm thinking she heard some ultrasonic sound from the movie. Wonder if the sounds were put in on purpose for this very reason. It would be a great idea, because the dog barking at the right moment was more scary than the movie itself.