When Leonard catches Sheldon cleaning Penny's living room in the middle of the night, Sheldon explains that he couldn't sleep knowing that outside his bedroom was the living room; and outside the living room was the hallway; and immediately adjacent to the hallway was ... "this".

Sheldon is a senior theoretical physicist at The California Institute of Technology.

A drunk Sheldon leaves wildly inappropriate voicemails for Stephen Hawking. At the end of the episode, several of the messages are heard on Hawking's answering machine, and Hawking can be heard calling Sheldon a jackass.

Howard 'only' has a Master's degree, while his three best friends all have PhDs.

In the episode "The Alien Parasite Hypothesis" Sheldon explains that 73 is the 21st prime number, its mirror, 37, is the 12th prime number and its mirror (21) is the product of multiplying 7 and 3, also in binary, 73 is 1001001, a palindrome.

Klingon Boggle is essentially the same as normal Boggle, but with pIqaD letters (Klingon script) replacing the standard Roman alphabet.

He got a cat that he named Dr. Robert Oppenheimer. Later, he got more cats and introduced them as Enrico Fermi, Richard Feynman, Edward Teller, Otto Frisch -- and Zazzles. Sheldon explained that he was going to call Zazzles Herman von Helmholtz, but "he's just so zazzy". Pretty soon, Sheldon had 25 cats and Leonard called his mother to come fix things before they got completely out of hand.

Unlike Sheldon, Missy displayed little to no interest or aptitude for schoolwork, especially math. She works as a hostess at Fuddruckers.

Leonard comes home to find Sheldon experimenting with luminous (glow-in-the-dark) fish. He plans to market them as night lights.

During a scavenger hunt, Amy and Howard bond over their shared love of Neil Diamond.