Doors

That's a door.

There are actually two doors, one larger one and one smaller one (you can see the two handles). Initially, the big one was for animals and the small one was for people. Then people stopped inviting animals into their houses, so they used the different knocks (which sounded different from each other) to differentiate who was knocking. If you were knocking and, if a woman answering the door had to be veiled, then you used the big knock. If she could answer the door unveiled (e.g. you were a member of her family), then you used the small knock.

Now you just do whatever you want.

As we (all 22 of us) were learning this, someone living in this house exited, looked at us oddly, then carefully locked his door and left. We continued staring at his door and talking about it in English.