The One With The Truth About London - S7-E16
Other mistake: Right at the very end, when Joey is in the fat-suit and picks up a piece of food and says "How you doin'?" he doesn't put it in his mouth, he just lifts it to his lips, stops, and tries to stay still. If this had been a freeze on the part of the director then fair enough, but it isn't as he and particularly Monica are still moving. It just looks rather corny and amateur, as though they are waiting for the "cut" to be called. (00:28:00)