There was another report recently about a fox sneaking in a house and resting in its living room. Due to the news report it was caused by the extreme cold weather. The fox didn't even bother the man sitting besides it. This happened in Germany but I know a few other similar reports (googled =)).

I've a hard time understanding what causes this extreme behavior. Why would a common fox sneak into a house full of humans just to get warm? Is this generally true? Or are these foxes either sick, habituated or tame to some degree?