
The One Where Nana Dies Twice - S1-E8
Continuity mistake: Just before the group of guys at the funeral shout about the football, there is a glass of wine next to Monica's mother which is about 1/3 full. After a brief cut away, the next shot shows the glass is almost empty. (00:19:05)

The One Where Nana Dies Twice - S1-E8
Continuity mistake: When Rach asks who the naked picture is of, the way she holds it changes between shots. (00:21:10)
The One Where Underdog Gets Away - S1-E9
Continuity mistake: When Rachel serves Joey coffee after he comes into Central Perk wearing make up, she puts the cup down on the far left hand side of the table. As Joey picks it up, it has moved to the far right hand side between shots. (00:02:45)

The One Where Underdog Gets Away - S1-E9
Continuity mistake: When Rachel gets her mail off Monica she puts it down on the couch and picks up a sealed envelope. The camera cuts and the envelope is now open with no time to open it. (00:07:25)

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)
The One Where Underdog Gets Away - S1-E9
Continuity mistake: Chandler is able to get into Monica's apartment to tell everyone that Underdog got away, but later when Rachel closes the door it is now locked. We can see the door as each person is leaving and nobody does anything which could be construed as locking the door before it closes. It's been often demonstrated in the show that the door doesn't lock automatically. (00:13:20)

The One Where Underdog Gets Away - S1-E9
Continuity mistake: At the end of the episode when Chandler makes a toast, he is holding the glass in his right hand. In the next shot, the glass has jumped to his left hand. (00:21:05)
Suggested correction: He switches the glass from right to left, so, unfortunately you're wrong.
The mistake is valid. While we do see him switching his glass between hands during the scene, when he says he's glad everyone's Thanksgiving sucked, he raises his glass in his right hand. In the next shot it's switched to his left and lowered a bit. Since this happens between shots (and he's not off camera), it means no time elapsed, so there's no time for him to switch hands again (in the submitted pictures, the bottom picture is the first shot and the top picture is the 2nd shot).
The One Where Underdog Gets Away - S1-E9
Continuity mistake: When the six are looking out the window at Ugly Naked Guy cooking his turkey, they are looking straight across the alley into his window. In "TOW The Giant Poking Device", Ugly Naked Guy's apartment is several floors below theirs in the adjoining building.

The One with the Monkey - S1-E10
Continuity mistake: Just before the opening credits, when Ross says, "That's 'pathet', which is Sanskrit for 'really cool way to live', " Marcel is sitting on Ross's left shoulder in the closeup, but in the next shot the monkey is suddenly sitting on his right shoulder, right before Ross walks off screen. (00:01:00)

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 with the Monkey - S1-E10
Continuity mistake: When Rachel says about her 6th date with Paulo, she is holding a decoration for the tree. In the next shot the decoration changes to a much larger object. Then, in the next shot, as she hands it to Monica, it has turned back to the original shape. (00:05:40)

The One with the Monkey - S1-E10
Continuity mistake: When Ross say 'just a smidge' after Rachel says Paulo named her breasts, Phoebe is holding tinsel and Rachel is looking at Ross. In the next shot, Rachel is looking in the opposite direction and the tinsel has vanished from Phoebe's hands. (00:06:00)

The One with the Monkey - S1-E10
Continuity mistake: Just after Chandler explains the situation to Janice, she goes off crying, and Ross takes a photo. The flash is much brighter than it should be - the screen's whited out to disguise a jump cut - after the flash Chandler's noticeably further back than he was before. (00:17:45)
The One with the Monkey - S1-E10
Continuity mistake: When David kisses Phoebe in the lab the first time, he writes "yes" on the board. Later on when they are in the lab again the "yes" is different than the previous one.

The One with Mrs. Bing - S1-E11
Continuity mistake: While everyone's at the restaurant Rachel dips a tortilla chip into guacamole and gets some on her hand. When Paolo takes a bite from the chip he also eats the guacamole off Rachel's hand while she's still holding the rest of the tortilla chip, but in the next closeup Rachel's hand is empty, then in the next shot the remaining tortilla chip reappears in Rachel's hand. (00:06:45)

The One with Mrs. Bing - S1-E11
Continuity mistake: When they are all eating at the restaurant and Mrs. Bing is telling Rachel how to write a book, the amount of food on Rachel's plate changes between shots without her touching it. (00:06:55)
The One with Mrs. Bing - S1-E11
Continuity mistake: The position of Mrs. Bing in relation to the pay phone keeps changing during her conversation with Ross at the restaurant. (00:08:55)

The One with Mrs. Bing - S1-E11
Continuity mistake: When Joey says to Ross in the hall 'you didn't call and leave your grip size' his arms are folded. In the next shot, his arms are behind his back. (00:10:20)

The One with Mrs. Bing - S1-E11
Continuity mistake: When Joey asks Ross 'how could you let this happen' in the hall, his sleeves are down to his wrists. In the next shot, they are rolled up. (00:10:25)

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)