Via MadArtLab comes this amazing optical/aural illusion that you have to see and hear to believe!
Cool, isn't it? I've heard (haha) of this illusion before -- it's called the McGurk effect -- but it's still fun to see it done this way. When the man is shown side-by-side saying it, switch your attention back and forth between them with each syllable. Even knowing it's an illusion, it's still overwhelming. I can't not hear it.
I would venture to guess that this is related to the audio version of pareidolia; seeing patterns in random shapes. This sort of thing is why people think they hear words when songs are played backwards, but that's completely wrong, just like seeing Elvis in a bit of reflected light. If you don't think this is possible, then simply watch this video of Carmina Burana and prepare to laugh your head off.
As always, the lesson here is that while we think our senses give us a clear view of the world, they not only don't, they can really screw it up. You can't always trust your what you see or hear! In fact, you rarely can. That's why we invented science.