The metal gallium melts in the palm of your hand.

Gallium is a solid metal at room temperature, but only barely — it melts at about 29.8°C (85.6°F), just above typical skin temperature. Hold a small piece in your hand for a few minutes and it will turn to liquid, then re-solidify once it cools back down.

That low melting point makes gallium useful well beyond party tricks: it shows up in some thermometers, in low-melting alloys, and famously in gallium arsenide semiconductors used in LEDs and solar cells. Unlike mercury, gallium isn’t considered significantly toxic in normal handling, though its liquid form can stain skin and will corrode aluminum on contact.