Just sort of a silly "make the world feel more alive" idea, where during a cold snap "Sleeping bears" appear in mines. They're basically bears that won't aggro until you wake them up via-
Starting a stamp press
Mining
Chipping boulders
or a cave in
Attacked
and they'll have an animation of them laying down.
At which point they'll do everything they can to get you out of their cave so they can go back to sleep. They should give extra lard when butchered.
Just a little idea to make the difference between cold/warm a bit bigger, and generate tears of people who use wimpy mining alts.