If your dog has ever come up behind you and pressed a cold, wet nose right into the back of your knee, you've probably wondered just why, exactly, dogs' noses are like that — at least, once you got over the initial shock! You may have also heard it said that a cold, wet nose is a sign of a healthy dog, and a warm, dry nose is a sign of illness. But is it true? And why are dogs' noses cold anyway? Let's sniff out an answer to these questions.