Optical illusion!

I found this yesterday, and I'm glad that I can share it. If you look at the picture, then step back three meters, the faces seem to swap places. Go on, try it!

Did it work? I like this optical illusion. If somebody knows how it works, please feel free to post and tell me about it!

How about this one. This is a still picture, nothing moving.

Does it wave? I think I have the idea of how this one works, but I still think that it is cool!