Continuity: In the second season episode entitled "Yes, Monsignor", Alan is sitting at the kitchen table talking to his son Jake about a math test that Jake got a bad grade on. At the beginning of the scene Alan holds the open test in his left hand. When the camera switches back to him a second later the test is now in his right hand. Finally at the end of the scene the test is back in his left hand but is now folded.

Continuity: When ever Charlie is playing the piano, it is clear he is not.