1. Frequently, Leonard has no actual glass in his glasses.
2. Penny is the only one of the show's main characters whose last name is still a mystery.
3. Mayim Bialik is the only cast member with a PhD: In 2008, she received her advanced degree in neuroscience.
4. Penny has been using the same purse on the show since the second episode of the first season.
5. The line in the show's theme, "Autotrophs began to drool," is a purposeful error/joke: Autotrophs are life forms like plants or algae that create their own energy, and therefore don't need to eat.
6. The actors actually learned how to play the instruments their characters play on the show (theremin, cello, harp).
7. Melissa Rauch based her character's voice on her mother's, "Only without the Jersey."
8. Sheldon's "soothing song," "Soft Kitty," is based on an Australian children's song from executive producer Bill Prady's daughter's preschool.
9. Jim Parsons has never seen Star Trek or Doctor Who, a fact that would be seriously depressing to Sheldon Cooper.
10. Briefly, a complete rip-off of the show called The Theorists was aired in Belarus. When the actors discovered they were performing in a stolen show, they all quit, which negated the need for legal action from BBT's creators.
11. Kunal Nayyar (Raj)'s wife, Neha Kapur, is a former Miss India.
12. There's a species of Brazilian bee named for the show: Euglossa bazinga.