DTS (Dry Tongue Syndrome)

A naturally occurring medical condition in which an animal is sleeping, the tip or part of their tongue then extends out of their mouth causing dryness on that part of the tongue, which normally requires retraction or licking upon waking up to remove the dry feeling. This can occur to any part of the mouth, but is generally in the direction of gravity. This is a common condition in dogs, cats, and some larger zoo animals. It may also occur to humans who are in a very deep sleep, or a deep sleep due to intoxication or other un-natural reasons.

The symptom is extremely relative to a human sticking their tongue on a frozen poll.

Man, look at Rover, he always has DTS (Dry Tongue Syndrome) after he falls asleep on the couch! Poor dog.....