In the winter, our breath smokes because of the cold, so why shouldn't the toilet's cold water? If you smoke, it's possible that the smoke is not ALL coming out the way it went in. I used to eat a meal 5 minutes after I had a cigarette and smoke would come out when I burp. It's gotta be something reasonable (of course, don't bring a cigarette into the bathroom, the stools give off methane, COOKING GAS). That's what caused the Chicago Fire...joke.