Gallium is a silvery metal with atomic number 31. It’s used in semiconductors and LEDs, but the cool thing about it is its melting point, which is only about 85 degrees Fahrenheit. If you hold a solid gallium crystal in your hand, your body heat will cause it to slowly melt into a silvery metallic puddle. Pour it into a dish, and it freezes back into a solid.
While you probably shouldn’t lick your fingers after playing with it, gallium isn’t toxic and won’t make you crazy like mercury does. And if you get tired of it, you can melt it onto glass and make yourself a mirror.