Continuity mistake: In the scene before Jay hits Phil in the face with the plane, the remote control's antenna (the one he is using to fly the plane) switches between the 'forward' and 'up' positions. (00:10:50)
Continuity mistake: Claire takes some cookies out of the oven and puts them on a cooling rack. When Manny asks her what the matter is with Claire, she holds still while she's about to put down the second cookie in the top row. When the camera cuts to a different angle there are suddenly three cookies in the row already. (00:12:05)
Continuity mistake: In the scene where Claire and Manny are discussing how they are brother and sister, Claire is placing cookies on a cooling rack from top to bottom. When the shot changes they are now placed left to right.
Answer: He has seen himself dancing, and is mortified at how bad he looks.