Speaking of eyes following you around the room, this Dragon Optical Illusion is pretty cool. You make it out of paper and sellotape, and move around it with one eye closed. The head seems to move and follow you around. (There’s a PDF to make the model, and a video to watch if you can’t be bothered.) Here’s the one I made:
The head’s actually folded inwards, but we’re so used to 3D objects bulging outwards that we see the model as if it’s moving instead of its true shape. You don’t even need to close one eye–from a few feet away it’s pretty compelling. A neat instance of the visual system’s assumptions dominating our current knowledge.
Mind Hacks 
Yeah, that little dragon is wonderful. I’ve given it as birthday present for years now, I’ve even managed to bring it twice (forgot about the previous year). When I travel and need a little gift, I pack the paper, scissors & glue, because the dragon once built is delicate.
A tip: put the dragon into a bowl (like a goldfish, no water though). Effect is even stronger.
I’ve also found there are 2 classes of people in their reaction to the little dragon: (a) aha, and then they turn away, (b) wow! and get really excited.