I've been wondering how many times do people knock on doors to get the attention of the person inside. I don't mean how many times a person knocks and then waits for an answer (and if none, knocks again). I mean, specifically, in each instance of knocking, how many knocks in a row.
I find that I was knocking twice. Then, I wondered about it. Wouldn't one knock be more efficient? So, recently, I've been knocking once. I noticed two things. First, it made me realize that knocking once sounds like something may have hit the door. But, when there is a double knock, it is more likely to be a person. Also, people don't respond as well to one knock. I assume for the above reason.
I know some people knock three times. I wonder why.