Hand your friend a glass of water with an ice cube floating in it, a piece of string, and a salt shaker, and ask him to lift the ice out of the glass without touching it. Sound impossible? It's not, here's how you do it.

When your friend gives up, take the string and lay it across the ice cube. Sprinkle a dash of salt onto the ice and wait for about a minute. Now, pull the string, and out comes the ice cube!

Why?

Salt lowers the freezing point of the ice, making it melt. At the same time, the ice tries to take heat away from the string which causes it to freeze to the ice cube. This is why people put salt on icy sidewalks and roads-- it melts the ice.