After Sheldon tells Penny he is not capable of keeping secrets, she tells him to "just forget about it". To this, Sheldon replies: "Forget? This mind does not forget" and explains how he has not forgotten anything since his mother stopped breastfeeding him. However, later in the episode he forgets about Lee Meriwether being one of the Cat women and about Professor X and Nightcrawler being two of the X-men.
Sheldon is folding clothes in the laundry room. He puts down a blue t-shirt on his folder in a close up shot. Next shot is pulled back and there is a pair of socks on the folder. Next shot he is picking up the blue t shirt to fold again.
The address for Howard's house has changed. In Season One's "The Dumpling Paradox", the address was 3150, as seen to the left of the door, below the porch light. Now, and for the rest of the show, the address is 845, as seen to the right of the door. Given that Howard "sleeps in the same room where his bassinet was" (as stated by Leonard in "The Maternal Capacitance"), it is obvious that the Wolowitz's could not have moved.
When Leonard and Sheldon come home from work carrying their bags, as they're arguing while they walk in the door, Leonard's right hand is twitching slightly. It then cuts to a closer shot of him and his hand is still.
When Sheldon comes over to stay at Rajesh's place, Rajesh is watching a Hindi movie and a song is audible for a few seconds. Sheldon asks Rajesh if that actress is Aishwarya Rai Bachchan and Rajesh says she is. But the song is from the movie Kaho Naa... Pyaar Hai which does not star Aishwarya Rai at all. At the start of the scene there is one more piece of music that is heard - a classical Indian tune. The music is never played in the movie, or at least, it is not played any time near the two occurrences of the song.