It's easy, as nikfrozty said, you actually give the character 2 heads, and one of them dissapears every so often. In the original models, they just had an extra poly in front of they eyes that was textures with the eyes and transparenc-ized, and they blinked on and off. I think this is the case, anyway. You can check Apz' old threads to see how he did it with his first model.