This episode establishes Sheldon's fear of birds.
Raj: On Sheldon's test, what did you guys put for his favorite amino acid?
Howard/Leonard: (together) Lysine.
Raj: I had lysine and changed it!
Penny: What is this?
Sheldon: It's a questionnaire I devised. I'm having some difficulty bonding with a colleague at work, so I'm doing a little research to better understand why my current friends like me.
Penny: Yes, well that is a good question.
Sheldon: Oh, good, you are just in time. I believe I isolated the algorithm for making friends.
Leonard: Sheldon, there's no algorithm for making friends.
Wolowitz: Hear him out. If he's really on to something we can open a booth at Comic-Con, make a fortune.
Kripke: Hello, I'm Barry.
Kripke: Ahh, it's not a very hot name. I'm gonna call you Roxanne.
Wolowitz: Suddenly I'm looking pretty good, eh?
Kripke: So what's the plan, Cooper?
Sheldon: Well, it's not exactly a plan, but I think I'm going to pass out.
(Sheldon passes out)
This episode's end titles has Chuck Lorre's Vanity Card #237, a mathematical explanation of Sheldon's "inverse tangent approaching an asymptote" joke.
The German episode title is "Der Freundschafts-Algorithmus", the French title is "L'Algorithme de l'amitié", the Spanish and Mexican title is "El algoritmo de la amistad", and the Italian title is "L'algoritmo dell'amicizia", all exact translations.
Music: "Sweet Georgia Brown" whistled by Leonard, Howard, and Raj
International Airdates: Latin America: March 10, 2009 on Warner Channel; Australia: August 10, 2009 on Channel 9; Turkey: November 30, 2009 on CNBC-e; Finland: January 4, 2010 on Sub; Czech Republic: November 11, 2010 on Prima COOL; Slovakia: September 30, 2011 on Markiza
When assessing the climbing wall, Sheldon says the wall appears monolithic, and he expects to see Hominids start using bones as weapons, referring to the opening segment of Stanley Kubrick's 1968 film, 2001: A Space Odyssey, "The Dawn of Man".
Leonard's suggestion that Sheldon would have better luck making friends if he waits until the Cylons take over is a reference to the main enemies from the Battlestar Galactica franchise.
A "raccoon with an distended scrotum" (as Wolowitz drew on Sheldon's questionnaire) is known in Japan as a tanuki, a mythical mischevious raccoon-like creature with shapeshifting abilities. Statues of tanuki are placed outside of buildings to ensure good luck.
Penny refers to Sheldon as, "Ichabod," comparing him to Ichabod Crane from Washington Irving's 1820 short story, "The Legend of Sleepy Hollow".
Leonard says to Penny that Sheldon doesn't have hope of making a friend unless he builds him, "out of wood, like Geppetto," referring to his creation of Pinocchio. Both characters are 1883 creations of Carlo Collodi.