Following the commercial break in this episode, Monica and Phoebe are waxing their legs with strips and are taking them off in a lot pain in which Joey and Chandler come in to see what is going on. After Joey says that women have a lower threshold of pain than men Phoebe puts a wax strip on his arm to see if he can stand the pain.

When she puts it on, notice how she puts it on. The strip is completely on Joey's right arm at one time but then the next time after he says "and I pull it right off?" part of the wax paper is on his shirt which wasn't there before.