Thats a good one and making mental note on Mentos for when the grankids come up. I love to broaden their already devious little minds and consider it payback for the frustrations their parents put on me.
A neighbors kid learned and a good one I wont show them though. He filled a 2 liter bottle with strips of aluminum foil then added toilet bowl cleaner and screwed the cap back on. The resulting pressure distorted the bottle till it blew and the concussion set off the hydrogen gas formed. (I couldnt believe the how violent the explosion was and loudness given it was a plastic bottle.)