The drinking bird is a toy that is also an example of a heat engine. It is a glass bird with a long neck that dips into water. The bottom of the bird is covered in a cloth that is soaked in water. When the bird’s head is tilted down, the water from the bottom wets the top of the head. As the water evaporates from the head, it cools down and causes the vapor inside the bird’s body to condense, which lowers the pressure. This makes the bird’s bottom tip over, and the water from the cloth is able to flow back into the bottom of the bird. This, in turn, makes the bird’s head tilt back up, where it starts the process all over again. So, the drinking bird is a simple heat engine that converts thermal energy into mechanical energy.