The One with George Stephanopoulos - S1-E4
Continuity mistake: The facial expression of the receptionist changes drastically between instant cuts when she says the line "any minute now" (00:14:00)
The One with George Stephanopoulos - S1-E4
Continuity mistake: The way the receptionist in the hospital holds the candy bar differs between the several camera angles. (00:13:30)
The One with George Stephanopoulos - S1-E4
Continuity mistake: When Ross gets hit with the puck, we see it flying towards him. Camera cuts and the puck has simply vanished and yet Ross acts as though he has been hit. (00:12:45)
The One with the East German Laundry Detergent - S1-E5
Visible crew/equipment: When the horrible woman enters, a tape marker is visible on the floor by the machines. (00:11:20)
The One with the Thumb - S1-E3
Audio problem: When Monica is first seen in the kitchen complaining about taking a guy home, the other chef is cutting some items up. However, the audio of the knife clicking as it hits the board is overdubbed. (00:08:00)
The One Where Monica Gets a Roommate - S1-E1
Visible crew/equipment: We get a close-up of the coffee pot when Rachel asks if anyone would like some. In this shot, there are 3 stage lights reflected clear as day. (00:27:50)
The One Where Monica Gets a Roommate - S1-E1
Continuity mistake: Near the end when Phoebe says to Monica, "C'mon give me your feet" she puts the red pen down on the blue paper. When Monica sits down though, the red pen is on the table and not the blue paper. (00:23:40)
The One Where Monica Gets a Roommate - S1-E1
Continuity mistake: When Joey makes the joke about Ross being 8, Ross has his right left hand lowered. Camera changes to a different angle and it's raised, before switching back to the 1st angle and being lowered again. (00:15:50)
The One Where Monica Gets a Roommate - S1-E1
Continuity mistake: The way Ross holds the can of beer changes between the full on shots and the shot of Chandler and Joey when just the can is visible on the side of the screen. (00:12:40)
The One Where Monica Gets a Roommate - S1-E1
Continuity mistake: When Joey hides the bracket in the plant pot, the instruction sheet that is on the bookcase disappears instantly. (00:12:20)
The One With the Baby on the Bus - S2-E6
Continuity mistake: When Chandler and Joey fetch Ben from the Department of Health Services, as they say they're both the baby's father, Chandler puts his arm around Joey and Joey takes his hand. When the angle changes you can see Joey's shoulder and Chandler's hand isn't on there. When it cuts back to the front view, his arm is around Joey again. (00:15:10)
The One With Barry & Mindy's Wedding - S2-E24
Continuity mistake: Phoebe takes out her gum before kissing Joey. After she kisses him, she makes a comment about it and her mouth is empty. In the next shot, she sits down and is chewing. But she doesn't put the gum back in. (00:02:22)
The One With Ross' Step Forward - S8-E11
Other mistake: In the opening scene when Rachel says "I went from store to store sitting on Santa laps" the camera is out of focus.
The One With Phoebe's Rats - S9-E12
Continuity mistake: When Gavin and Rachel are in Rachel's office, in some shots Gavin is wearing a wedding ring. (00:03:43)
The One With the Holiday Armadillo - S7-E10
Revealing mistake: When Ben sits on the sofa to listen to Ross talk about the festival of lights, you can see Monica move Ben to the other side of the sofa despite there being space for her to sit. This is so they sit in the correct order as she would mask Ben to the cameras.
Continuity mistake: When Phoebe goes to visit her mom for the first time, she takes a cookie from the cookie jar and leaves the lid off. But in one shot, the lid is back on. The lid is back off in the following shots. (00:06:36)
The One With The Princess Leia Fantasy - S3-E1
Other mistake: When Phoebe makes fun of Ross' Princess Leia fantasy with the rolls, Rachel tries to stop her; the shots used are the same action, just from different angles. Look at Rachel's hands and the towel in her hand when Phoebe puts the rolls by her ears.
The One In Barbados, part 2 - S9-E24
Continuity mistake: As Mike and Monica are playing ping-ping, two people playing checkers magically materialize behind Monica. One second they're not there and the next second they are. (00:12:25)
The One Where Everybody Finds Out - S5-E14
Continuity mistake: When Monica and Chandler come in to ask Joey about Pheobe knowing about their relationship he throws the Hugsy teddy behind him. In the next shot we see behind the chair and Hugsy is not there.
The One With The Free Porn - S4-E17
Other mistake: 10:50pm boarding and departure, but it is broad daylight outside. (00:09:25)
Answer: Usually by the seventh night of Hanukkah you don't know what to get the other person, and you will probably resort to getting the other person something insignificant. Chandler is basically saying that the pen is a stupid gift.