An exotic bit of hand blown glass with a bulb at top and bottom connected by some zippy tubing that spirals, loops, and/or jogs. In the closed system is some colored liquid (methylene chloride) that is very light. Hold the lower bulb in your hand and as the liquid is warmed it pushes through the loops to the upper chamber. When all the liquid is pushed out of the lower bulb, expanding air will bubble through the tubing making it appear that the liquid is boiling.
This product is glass. Colors ship random.