Continuity mistake: Rachel is talking to Joey in his apartment after waking up the next morning, looking messy and rumpled. As she talks, her bra strap slips down her arm. In one shot (as she says "I'm a horrible person"), the strap is all the way down her arm and then in the next shot it is tucked under her shirt. (00:10:00)
Continuity mistake: After Chandler has written the message on the Magna Doodle, the sliding eraser moves from the right to left side just as he leaves with Monica, and when Joey and Chandler are playing foosball, the barely legible "Joey" is now neatly written on the Magna Doodle, and its sliding eraser is again back to the right side.
Continuity mistake: Just before Chandler gives Monica the mixed tape, he tries to manipulate a coat hanger into something feasible. He stretches it out and holds it up, saying "Yes, honey, I made it myself," then the camera cuts to another angle as he throws it down. After the cut the hanger is not as stretched as it was before. (00:10:40)
Continuity mistake: In the previous episode, Monica's Christmas tree is up in her apartment. After the party, Joey kisses Janine. In the next episode, he walks into Monica's apartment and says he just kissed her. However, Monica's tree is down and they have all changed their clothes. Surely if he just kissed her then it is still the same night of the party, therefore the tree should be up and Monica, Ross and Joey should be wearing the same clothes from the party. (00:00:05)
Continuity mistake: When Monica is in Richard's apartment she gets all worked up, so Richard gives her a hug to calm her down. She goes into the hug with her arms curled up in front of her face, but when the camera angle changes, they are at Richard's back. (00:13:50)
Continuity mistake: When Chandler throws his copy of "Chicken Soup for the Soul" under the sofa and it goes across the floor to Monica's feet, she kneels down to pick it up by the counter next to the door, but when she rises, she's next to a chair that's under the table. (00:12:20)