It neat, it's educational, and best of all, it doesn't involve anything that could explode or become poisonous or make a terrible smell.
A surprising phenomenon sometimes occurs to people who have lost a hand. Soon after the hand is lost, they report that they can feel it again, this time when something touches the side of their face. A neurologist can lightly touch different areas on the cheek, for example, and the person will say it feels as if two spots were being touched simultaneously. One on their face, and one on their missing hand. Learn more on this Moment of Science.
Did you know what the eyes of a bird are fixed immovably in its skull?