Talk:Sheldon Cooper/@comment-77.102.31.161-20120709013519/@comment-5274094-20120709114845

According to IMDB, the first time Sheldon does multiple knocks and uses the person's name is in Season 1 Episode 10, "The Loobenfeld Decay".

"Although rather than the usual 3 short knocks, followed by asking someone's name, repeated three times over, it is 4 short knocks, followed by asking someone's name."

I did not find when they refined it to 3 knocks.