Sound, Speech, Sine Waves, Perception, and our Brains.

This stuff is kind of hard to explain, but once you experience it, it will be very clear.

First, listen carefully to Sound Clip A. What does it sound like?
Now listen to Sound Clip B. Then, listen to clip A once again.

Crazy huh?

Here are a bunch more just like that, exact same procedure:
Clip A ------> Clip B
Clip A ------> Clip B
Clip A ------> Clip B
Clip A ------> Clip B

These are all from Matt Davis's article An Introduction to Sine-Wave Speech.

Via the Music of Sound.