The One With Two Parties - S2-E22
Continuity mistake: When Chandler and Joey are in Monica's apartment blowing up balloons, Chandler's balloon changes type. The camera changes and it goes from shiny to dull. (00:03:30)
The One With Two Parties - S2-E22
Continuity mistake: Just after Rachel goes in to her surprise party in Chandler's apartment, she is talking with Ross and Chandler and says, "Both of them are here?" As she says this, she is facing forwards, yet in the next shot, she is suddenly facing Chandler. (00:08:15)
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