I understand that when you put your tongue on frozen metal, your tongue sticks to the metal but how does having a layer of ice covering the metal prevent your tongue from sticking?
When you touch your tongue to metal colder than the freezing point of water, your saliva freezes and your tongue gets stuck. The metal conducts away the heat from your tongue. When there is a layer of ice covering the metal the ice partially melts when your warm tongue touches it and your tongue doesn't stick. The ice is not nearly as good a conductor of heat as the metal.