In TWO where Carol gets married to Susan, Rachel is nervous about her mother coming to visit and accidentally brings her friends dirty, half-drank cups of coffee and Chandler says "I ordered the coffee with a cigarette floating in it" or something like that. In TOW Chandler takes up smoking, Gunther tells him he can't light up his cigarette in the coffee house. If you can't smoke in there, how did the cigarette butt get into the coffee cup?