Step 1: What You Need:
- A good-natured victim
- OK story-telling skills
Step 2: Setting the Stage
- Explain to them; "The ancient Romans used to think that intelligence depended on the size of the brain. To test someone's intelligence they would take a coin, press it against their forehead and have them hit themselves on the back of the head, trying to knock it off. They they thought that people with larger brains had them pressed tighter against their skulls, so the shock of hitting the back of your head would carry through easier and knock the coin off. They counted how many hits it took to knock the coin off, and the less hits it took the smarter you were."
- Take out a coin. Frown and squeeze your eyes shut tight (it's important you do this so when you tell your victim to they won't be suspicious). Then press the coin against you forehead, take your hand away, and open your eyes.
- Hit yourself on the back of the head, counting each hit, until the coin falls off.
Step 3: Executing the Prank
- Tell them to frown and squeeze their eyes shut. If they ask why, say something like "you need to do it to get the skin on your forehead tight so the coin sticks.".
- Press the coin hard against their forehead and carefully pull it away. They should feel like they have a coin stuck on their forehead.
- Tell them to open their eyes and start hitting themselves on the back of the head. If you want, pass them things that won't hurt them to hit their head with.
- When you feel like they've had enough or they seem really frustrated, show them the coin and explain.