The One With The Giant Poking Device - S3-E8
Continuity mistake: At the end when Chandler is singing "Endless Love", Phoebe comes in and when she walks over to Chandler he has his arms wrapped around the Lionel Richie record with the shoe in his hand in front of the record. When the shot switches to just Chandler, his right arm is resting on the arm of the chair and his left arm is holding the shoe behind the record. (00:21:00)
The One With The Giant Poking Device - S3-E8
Continuity mistake: At the start, Phoebe snaps at Rachel that she will go to the dentist. When she says this, her grip on the apple in her hand changes between shots. (00:02:30)
The One With The Giant Poking Device - S3-E8
Continuity mistake: When Ben says Monica's name she's holding the Minute Maid juice box, but in Ben's closeup the juice box is on the table, though it's back in Monica's hand in the next shot. (00:08:50)
The One With The Giant Poking Device - S3-E8
Continuity mistake: When Chandler is breaking up with Janice and she walks away trying to shake him off, her jumper is untied. When Chandler says "You can't go, I have your shoe" we cut back to Janice and her jumper has been tied at the bottom.
The One With The Giant Poking Device - S3-E8
Continuity mistake: When Rachel and Monica are stressing about the bump on Ben's head, Rachel's hair keeps moving from tucked behind her ear to hanging loosely in her face between shots.
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