Add Yahoo as a preferred source to see more of our stories on Google. Sheldon knocking on a door on The Big Bang Theory - CBS "The Big Bang Theory" featured many recurring habits that defined Sheldon ...

"The Big Bang Theory" featured many recurring habits that defined Sheldon Cooper (Jim Parsons), but few were as consistent as his practice of knocking on doors three times — most often when visiting ...

An error has occurred. Please try again. With a Lewiston Sun Journal subscription, you can gift 5 articles each month. It looks like you do not have any active ...

No matter how early in the morning or how late at night, you can turn on the TV and find "The Big Bang Theory" playing on at least one, if not multiple, channels. And that's not even counting the show ...