Sheldon mentions that Howard used university resources to build a six-breasted sex robot. It can be assumed this is the 'Lisatronic 3000' mentioned by Leonard in The Holographic Excitation (2012).
Penny becomes exasperated with Leonard's multiple references to Star Trek's Captain Kirk, including an impression of William Shatner. This episode originally aired January 3, 2013, the same week that it was announced that Kaley Cuoco would begin appearing in Priceline commercials as the daughter of The Negotiator, a character played by Shatner.
Second appearance of Raj's Yorkshire Terrier.
The Giant Jenga game has 5 blocks/level, rather than the traditional 3. Based on the position of the tower, when Alex arrives, the solid starting tower would be 18 levels for a total of 90 blocks. A traditional game also has 18 levels, but in a 3 blocks/level format, for a total of 54 blocks.