Put an ice cube in a glass of water.
Take a match, lay it across the ice and try to lift the ice up with the match.
Lay the match on the ice again and scatter a pinch of salt over the match.
Count to 10 and lift the match.
Salt water does not freeze as easily as ordinary water, and scattering salt on ice makes it melt. When a substance melts, heat is consumed at the same time. This heat is taken from the moisture under the match, where no salt fell, in this case – and it freezes.