First physical appearance of Ira Flatow on the show. His voice was heard on The Vengeance Formulation (2009) while he was also interviewing Sheldon.
Sheldon makes a fuss about Raj's dog in the apartment because in The Plimpton Stimulation (2010), he stated that pets are banned under The Roommate Agreement, with the exception of service animals, such as seeing eye dogs and, one day, "cybernetically-enhanced helper monkeys."
Sheldon talks about having 9 friends, 10 if he counts (Howard) Wolowitz. These friends are: Stuart from the comic book store, Raj, Amy, Bernadette, Penny, Leonard, Arthur/Professor Proton, Barry Kripke and Wil Wheaton
Kripke accuses Sheldon of making fun of his speech impediment. In other episodes Kripke seems to be unaware that he has a speech impediment. For example, he doesn't understand why Siri can't understand him.
Title Reference: Leonard disproves the existence of the heavy element that Sheldon discovered in The Romance Resonance (2013).