Explanation: When someone double-dog-dares you to lick a flagpole in the dead of winter, you should politely decline — especially if that pole is made of metal.
The danger here lies in metal's conductivity. When the temperature drops, cold metal can draw heat out of your tongue's saliva and freeze its water content, basically transforming your spit into a kind of superglue. Your textured taste buds also help grip the chilly surface, which only adds to an already uncomfortable bonding experience. Try the same maneuver on a smoother body part (no clinging texture) or a plastic pole (less heat conductivity), and you'll be free and clear.
But once your tongue strikes metal, it may take a serious round of tug-of-war to get it back intact. If you value your sense of taste, it's probably best to just avoid the situation in the first place.