Well, this is the first winter weather with our Yellow Dog. Her teeth chatter when it is cold and she is excited. She is a senior and has a lot of flattened teeth, strangely more than any other dog I have had even ones living to 14 years old plus. It just makes me wonder how old she really is sometimes. Is this common? She just does it for like a second when she comes in from outside while she is doing the happy dance to see us again. Actually, if she out for 2 minutes................maybe she has a weak concept of time or we are just so darn wonderful that 2 minutes away from us seems like an eternity.