The One With The Chicken Pox - S2-E23
Continuity mistake: When Phoebe and Ryan are playing Monopoly, she rolls the dice and one goes off the board (but stays on the table). It then cuts to a wider view of them and both dice are back on the board. (00:09:50)
The One With The Chicken Pox - S2-E23
Continuity mistake: When Monica says about Richard not having a 'thing', her arms change place depending on the shot. (00:14:10)
Answer: The statements that she's contradicting (that it is common, it happens to every guy, and it's not a big deal), are the things that a woman commonly says to a man who is suffering from erectile difficulty, typically to assuage his bruised ego. However, most men do not believe that these statements are true, as evidenced by Chandler's outburst. He's so caught up in the proof that women are lying about it that he gives himself away.
Rooster of Doom