Here are two cheap physics toys that put on a fun show as you interact with them. The Horizontal Hand Boiler has two sealed glass bulbs that are connected by a narrow tube. As you hold one side, heat is transferred to the liquid inside through your hand, and pressure is increased on that side. That leads to the liquid going through the tube into the other side and creating a boiling effect. A vertical version of this is also available.
The Drinking Bird is even more fun. It is based on a very similar concept but creates the effect of a bird drinking for a cup. It has an internal tube and a water absorbing head. When water evaporates from the head, the pressure reduces, which leads to the liquid from the bottom side moving to the top. The rising liquid leads to the bird tipping and its beak reaching your water. The pressure keeps equalizing that leads to the bird going back and forth.
