This is the most common suggestion we get. Definitely not pens. The long walls are often not high. Some mustatil have gaps in the walls. Others run up the side of volcanos or steep hill. The entrance into the structures are tiny, most people would need to walk through sideways. Basically, we are positive that they couldn’t hold animals. We also have animal pens from later periods(and perhaps some now from same time) and they are very different. We have excavated 5 mustatil now, of a few different types. Other teams in the region have collectively excavated 4 and we compare results. We have also visited or photographed hundreds more. So we can be really certain about the ritual function. But you are right- the people who made these were shepherds. Moving around the area to take advantage of available grasslands etc. very similar to some of the Bedouin still today. Thanks for the question.