Sheldon states that he played Nintendo 64 in 1999 when he had pernicious anemia. This type of anemia is an inabilty to absorb vitamin B12. It's treated through B12 injections. Patients don't have to stay home or in bed, just get B12 directly.
When Sheldon's laptop's battery is dying and he returns to connect it to an outlet, he grabs only an extension cord, but not the computer's AC adapter.
When Sheldon told Leonard at the end of the show to "look at the bright side," he said Comic Con was only nine months away but it's actually ten months away as it always occurs at the end of July every year in San Diego.
Sheldon: Leonard is upstairs right now with my archenemy.
Penny: Your "archenemy?"
Sheldon: Yes: the Dr. Doom to my Mr. Fantastic, the Dr. Octopus to my Spiderman, the Dr. Sivana to my Captain Marvel...
Penny: Okay, I get it, I get it.
Sheldon: You know, it's amazing how many supervillains have advanced degrees. Graduate schools should do a better job of screening those people out.
Leslie: So, I heard your relationship with Penny crashed to the ground like blue ice falling out of an airplane lavatory.
Leonard: Where'd you hear that?
Leslie: Actually, I read it. Wolowitz texted me. (shows text message)
Leonard: "like blue ice falling out of an airplane lavatory" Yep.
Leslie: I thought it was a pretty good one. I gave him an LOL.
Sheldon: Why should I leave? This is my apartment, too.
Leonard: I know it is. And if science ever discovers a second member of your species, and you two would like some privacy, I'll be more than happy to get out of your way.
Sheldon: Everybody has a date. Even you Mario, going after Princess Peach. What am I doing? I'm just enabling you.
Raj: (to Leonard) What about [dating] Leslie Winkle?
Sheldon: Oh, no.
Sheldon: Her research methodology is sloppy, she's unjustifiably arrogant about loop quantum gravity, and to make matters worse, she's often mean to me.
Eric: Like your hat.
Wolowitz: Thanks, my mom made it.
This episode's end titles has Chuck Lorre's Vanity Card #217, which is actually a "censored" card redirecting people to view the genuine card rejected by CBS on Chuck Lorre's website.
The German episode title is "Sex mit der Erzfeindin", meaning "Sex with the Archenemy". The French title is "Le Flirt de Léonard", meaning "Leonard's Girlfriend". The Italian title is "La topologia del sospensorio", meaning "The Jock-Strap Topology". The Spanish title is "La topología de la bragueta", meaning "The Fly Topology". The Mexican title is "Clave topológica", meaning "Primal Topology"
With this episode, Sara Gilbert is elevated to the main cast, but is only credited when she appears in an episode.
International Airdates: Latin America: November 11, 2008, on Warner Channel; Turkey: September 14, 2009, on CNBC-e; Finland: October 19, 2009 on Sub; Czech Republic: October 25, 2010 on Prima COOL; Slovakia: September 14, 2011 on Markiza
Sheldon complains, "Leslie Winkle. Of all the overrated physicists in all the labs in all the world, why does it have to be Leslie Winkle?" playing on Rick's line about Illsa in Michael Curtiz's 1942 film, Casablanca, "Of all the gin joints in all the towns in all the world, she walks into mine."
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