Sheldon describes Raj's desk as a "brobdingnagian monstrosity", explaining that it is a British idiom. He's referring to the imaginary giants' kingdom of Brobdingnag in Jonathan's Swift's book "Gulliver's Travels". Brobdingnagian means excessively large.
The costume George Takei is wearing is the same costume he wears in Star Trek IV: The Voyage Home (1986).
Sheldon fills his office with hydrogen sulfide gas, which subsequently explodes when exposed to Raj's candle flame. This is a genuine chemical reaction: Hydrogen sulfide burns explosively when mixed with air to produce water vapor and sulfur dioxide.
The scene when Howard is "alone" with himself in his bedroom features the theme music from A Man and a Woman (1966), by French composer Francis Lai, who is possibly most famous as being the composer of the theme to the film Love Story (1970). It is performed by the piano duo of Art Ferrante and Lou Teicher.
No scenes occurred in Leonard and Sheldon's apartment.