Unburstable Balloon

Effect: You stick pins into an inflated balloon – but, thanks to your magical powers, the balloon does not burst.

Secret: The balloon has on it several pieces of clear adhesive tape. These will not be visible from even a short distance away. Push a pin into the balloon at one of the taped areas and the balloon will not burst (although it will go down after a while). You can push the pin into several different places to prove your magical ability. When you want the balloon to burst simply push the pin into an area that is not protected by tape.