(via) Listen to this wav file.

I'm guessing that it comes across as whistles and clicks, right?

Now, listen to this wav file.

Easy enough to understand, right?

Now, listen to the first wav file again.

Interesting, right? For more about what's going on, check out Matt Davis's Introduction to Sine-Wave Speech. There are also a few more sine-wave/clear-speech examples to check out (though the effect is less dramatic the more examples you hear, I found).