Have you ever gotten your fingers stuck to an ice-cube tray in the freezer or your tongue stuck to a flagpole in the winter? Yet, you can eat a totally frozen Popsicle without injury.

Why does flesh stick to some frozen stuff and not others?

Applying your tongue to a flagpole is definitely asking for it. The reason flesh sticks to metal is that the moisture on your skin freezes on contact, bonding it to the metal. Your tongue doesn’t stick to a Popsicle (for long, anyway) because the Popsicle warms up too fast. Metal is an efficient conductor of heat and can easily disperse the warmth from your fingertips, but ice isn’t and can’t. The surface of the Popsicle melts almost instantly when you lick it, whereas you have to warm up half the ice-cube tray before the surface under your fingertips rises above freezing. That’s one reason plastic trays have become such a popular substitute.

From The Straight Dope by Cecil Adams