The human brain is a freaky thing.  Sometimes it does amazing things.  Sometimes it malfunctions on a massive level and makes you not want to trust your own eyes.  Check out this little video, and you'll know what I mean.

When the video plays, you'll see a face on either side of the screen.  They're just regular faces.  But if you stare at the cross in the center of the screen, those faces will go CRAZY on you.  Like weird, mutant faces.  But when you focus on the individual faces themselves, you'll see they're completely normal.  This is just one of those messed up things our brains do when faces flash by and their eyes are aligned on the same level.  Don't try to figure it out more than that.  It'll make your poor brain hurt.

If you just have to know more about this effect, you can try reading up on it here and here.