Entertainment : 5 things you didn't know about The Big Bang Theory

1. “Soft Kitty” is a adapted version of “Warm Kitty,” a children’s song by Edith Newlin. 
2. Jim Parsons(Sheldon) learned to play the theremin for the character.
3. There is only one set of stairs leading up to Penny, Leonard, and Sheldon’s apartments.
4. Kaley Cuoco(Penny) and Johnny Galecki(lenard) dated for two years while they were costars.
5. Jim Parsons is responsible for Sheldon's laugh and smile.