Related to 18, you can also tell them that they can more quickly cool down a beer (or a juice box, depending on their age) by wrapping it in a moist paper towel before putting it in the freezer. The water, while evaporating from the towel, will draw heat away from the beer, thus making it cooler faster than if there were no towel.

And yes, water can evaporate even at low temperature, it'll just be at a lower rate. The above effect will thus be more efficient in the context of the cat in 18.