Continuity mistake: The morning after the second party, the items on the coffee table change instantly between shots. Several beer bottles and blue cups vanish, whilst a red cup and red bowl appear. (00:11:00)
You Can't Miss The Bear - S1-E1
Continuity mistake: When Nancy goes into her guest room with Silas and Quinne in it, the things she are holding change position in between shots. (00:28:35)
Continuity mistake: When Izzie is looking at the patient board, there are some lines on it which have been wiped out. But in the next scene we actually see Meredith walk to the board and wipe these exact same lines off (even though they were previously rubbed out...) (00:34:05)
Visible crew/equipment: During the scene where Dennis and the Waitress, Mac and Dee successively walk into the back office to talk to Charlie near the beginning of the episode, in some of the shots, you can see outside the office door, and you can see the top of the set has no ceiling, and even see part of a stage-light.
Roger Codger - S1-E6
Continuity mistake: In the Area 51 flashback, the "RESTRICTED" sign on the lab door goes from red to blue between shots. (00:11:00)
Continuity mistake: The dancer is eating some M&M's on Pam's desk. In one shot, there are some M&M's on the table in front of Pam. In the next, they are missing.
Killerball - S3-E18
Continuity mistake: When Randy laughs frantically after the Hensons told him they have been abused by a Dobermann, he's near a billiards table where there are two balls. At the end of the scene another ball appears on the table from nowhere.