Pop Top

Did you know that you can get a bottle to talk to you?  All you need is a bottle full of very cold water and warm hands.

Spill out the water.  The bottle looks empty but it isn’t.  It is full of very cold air.  If you heat this air with your hands it will need to escape by popping up the top (warm air takes more space than cold air).  When the warm air has escaped the top will pop back down again until more of the air heats up.  It looks like the bottle is talking!