Talk:Sheldon's Knock/@comment-136.234.105.211-20140411165425/@comment-67.241.9.199-20150419000251

It could be obsessive compulsive disorder, with the three knocks, name, repeat twice ritual being the compulsion.

However, Sheldon said to Penny in "The Communication Deterioration" that if Penny started it as well, she'd never stop; so it could just as well be a habit, if Sheldon does it unconsciously.