Hand Boilers are looped in the glass sculptures containing a liquid that will "boil" as heat is transferred from your bare hand. Simply hold the large bulb end on the bottom in the palm of your hand and within minutes, your body heat from your hand will cause the liquid to rise. Once out of your hands, it takes a few minutes for the liquid to cool down. Pretty fascinating science toy and an excellent demonstration of energy transfer. Additional Details ------------------------------ Product description: Hand Boilers are looped in the glass sculptures containing a liquid that will "boil" as heat is transferred from your bare hand. Simply hold the large bulb end on the bottom in the palm of your hand and within minutes, your body heat from your hand will cause the liquid to rise. Once out of your hands, it takes a few minutes for the liquid to cool down. Pretty fascinating science toy and an excellent demonstration of energy transfer.