The One Where Underdog Gets Away - S1-E9
Visible crew/equipment: When Chandler runs into the apartment to say Underdog has gotten away, a crew member can be seen reflected in the sun shaped mirror behind him walking through the back of the shot. It can't have been Rachel, Monica, Phoebe or Joey because Joey is sitting down and Rachel, Monica and Phoebe are nowhere near the mirror. (00:14:05)
The One Where Rachel Finds Out - S1-E24
Other mistake: When Rachel leaves the apartment to pursue Ross to the airport, she is turning to the left when she exits the apartment. The stairs are to the right.
The One Where Rachel Finds Out - S1-E24
Continuity mistake: When Rachel and Monica are discussing whether or not Rachel should meet Ross at the airport she's taking a bottle of red wine out of the refrigerator, but when she places it on the table in the next camera shot the bottle of wine is suddenly a bottle of white wine. (00:16:25)
The One with the Stoned Guy - S1-E15
Other mistake: Mid episode when Monica turns off the cordless phone after being told by Wendy that she can not make it, the phone makes the "out of range" audio tone instead of the "power off" audio tone. Occurs directly as Monica says, "Wendy, we had a deal, yeah, you promised. Wendy, Wendy, Wendy.".
The One with the Monkey - S1-E10
Visible crew/equipment: When Joey the Elf deliberately jingles his elf shoes, Chandler's head may explode because of all the unspoken mocking jokes. It then cuts to a shot of Marcel, and the trainer's hand is visible in the bottom left corner of the screen. (00:07:25)
The One with the Dozen Lasagnas - S1-E12
Other mistake: After Carol asks Ross if the lasagna is vegetarian, the camera briefly goes out of focus before Ross says "I'm pretty sure that it is." (00:05:00)
The One with Two Parts: Part 1 - S1-E16
Visible crew/equipment: When Phoebe knocks on Joey's door you can just see 2 orange T markers on the floor. (00:22:10)
The One with the Boobies - S1-E13
Continuity mistake: When Joey's mum explains that every day is like her anniversary, her hands are outstretched. Camera cuts and they are lowered. (00:18:20)
The One with the Boobies - S1-E13
Continuity mistake: The way Rachel is sitting when discussing seeing Chandler naked is constantly changing. (00:07:00)
The One with the Dozen Lasagnas - S1-E12
Continuity mistake: Second time we see Monica score on the foosball table, she spins the rod closest to the goal. The camera changes and the ball is hit from the rod furthest away from the goal. (00:17:35)
The One with Mrs. Bing - S1-E11
Continuity mistake: At the hospital, the positions of the balloons Monica brings change instantly. Note the blue one. Its height changes drastically from below to level with the yellow one. (00:11:30)
The One with the Monkey - S1-E10
Continuity mistake: When Phoebe asks the guys if there is something they would like to share with the group, David goes from looking at his friend to looking at Phoebe between instant cuts. (00:05:05)
The One Where Underdog Gets Away - S1-E9
Continuity mistake: When Rachel turns up with her tickets, Chandler has his hand on his hip. As Rachel walks off however, his arm is behind her. (00:12:00)
Continuity mistake: When Ross is reading the book he shows it to Phoebe who passes it back. Then without turning the pages he passes it to Chandler but the pages are different now. (00:07:20)
Continuity mistake: When Joey asks how the play was, Monica's grip on her program changes between shots. Note the gap between her hands. (00:04:20)
The One with Two Parts: Part 1 - S1-E16
Continuity mistake: Towards the end, as Joey is leaving Central Perk, Rachel's posture goes from leaving over the back of the sofa with her hands clasped to standing up with her hands on the back of the sofa. (00:18:15)
The One with Two Parts: Part 1 - S1-E16
Continuity mistake: When Rachel says about the name being the same in Spanish and English, the way she holds her chopsticks changes between angles. (00:06:10)
The One with Two Parts: Part 1 - S1-E16
Continuity mistake: When Chandler is saying how cute Nina is, Rachel has her hand in the bag of Chinese food. When the camera cuts, the hand is gone. (00:05:55)
The One with Two Parts: Part 1 - S1-E16
Other mistake: When the woman in blue walks into Chandler's office, the camera pans back a bit too far showing the edge of the set. (00:05:20)
The One with the Stoned Guy - S1-E15
Continuity mistake: When Monica asks for the gummy bears near the end, she has her hands by her side. As the camera changes, a hand is now visible raised that should have been visible before. (00:20:00)
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