Tricking the eyes is cool. One of the tricks we learned in grade school and was still cool in JR High was this: Stand in a narrow space, just wide enough for you to stand with your arms at your side. now, without bending your elbows push your arms out to the side against the wall. Keep this up with a high effort for about 45-60 seconds. Then step out of the small area and let your arms relax. The crasiest thing is that when you relax your arms will start to rise on their own. I've shown kids this and not told them the outcome, and when their arms start to rise on their own the kids freak out and then go show other kids.