Continuity mistake: During this whole episode, Jake calls his mother's boyfriend Greg. But in the 4th season when Judith is marrying the guy, he is called Herb. We know that it is not two different people because they both have the last name Melneck, and they are both Jake's pediatrician.
Continuity mistake: Alan throws a bra onto the floor after Charlie tells him whose bra it is, which lands touching a rug. Alan goes to pick it up and the bra has not only moved away from the rug but it is also lying in a different position. (00:12:00 - 00:12:40)