Continuity mistake: When Annie starts to throw her tantrum, she knocks stuff off the table, including the microphone and small mic stand. When she's lying on the table, the mic stand is back on the table. It back on the floor when she and Jeff leave, although the Uruguay sign is now back on the table.
Continuity mistake: When Britta is in a cage, before Chang walks in, a couple pass her and are walking out the double doors, where both doors are open. After Chang steps up to the cage and the camera shot changes, the couple is further away from the doors and walking out again, only this time one of the doors is closed.
Visible crew/equipment: At the beginning of the episode, after Pierce rejoins the group and Jeff and the others begin to leave the room, watch Britta as she stands up. When she turns away from the camera, you can see the actress' microphone-pack in the back of her jeans briefly. (It's hard to spot but it's there, and is confirmed in the commentary track.).
Other mistake: During Leonard's "Let's Potato Chips" YouTube video during the ending credits, you can see the video reaches the end of the load/play bar (watch the circle), yet the video continues for several seconds. Once the circle reaches the end of the load/play bar, the video is over and won't continue.
Character mistake: In the bonus clip where we see Leonard's online video about frozen food, the first thing he says is, "This is November 29th". However, if you look under the video, you can see the video was uploaded on Nov 26, 2011, which is three days earlier.