Amy informs Penny that the iconic heart shape is actually based on the shape of a female’s buttocks when bending over. The Alien Parasite Hypothesis | The Big Bang Theory Wiki
Sheldon’s preferred theory, as he finds it more plausible than the final option. [S4E10] The Alien Parasite Hypothesis
The "cold, harsh truth" they eventually accept. Iconic Moments & Quotes Amy informs Penny that the iconic heart shape
Sheldon famously declares 73 the "best number". It is the 21st prime number. Its mirror (37) is the 12th prime. In binary, it's a palindrome: 1001001 . Iconic Moments & Quotes Sheldon famously declares 73
Howard and Raj fight over who would be the superhero and who would be the sidekick after a lab tech is bitten by a radioactive rat. Production Trivia
Dismissed by Amy (despite Sheldon's "testy bark of an old biddy" comment).