It's a hot day, so why not make a mess.
Mix about 1/2 cup water with 2 cups cornstarch. It's a solid and a liquid.
Cover your hand like a glove, it is weird and cool and best of all, it washes off easily at least the starch part (see below).
Cut it in chunks and watch it melt back together.
We had a lot of fun poking and prodding it, molding and melting it. It is so interesting and bizarre and kills a few boredom bugs.