not a command - an action

***if something is thrown over your head remain silent and motionless until it is removed by a FreePerson.

Book 13, page 94
Not a particular position, but rather, a condition. The Master places a blanket over the slave, which indicates that the slave shall remain still and silent beneath the blanket until the blanket is removed

Book 13, page 94
I then threw the second blanket, the top blanket over her, covering her completely. When a blanket, or cloak, or covering of any sort, is thrown over a slave like this she may not speak or rise. She must remain as she is, silent, until the master, or some free man, lifts the covering away.