Shorts borrow shares from longs. There has been much discussed about how to prevent. But they borrow at a high point, then manipulate the stock down using a variety of tactics. But here is the key INVESTORS PANIC SELL AND CREATE THE DOWNWARD MOMENTUM. The goal of the shorts is to buy toward the bottom.

They watch it closely because investors like myself buy back in as well. My goal is to take some of their profits. Of course, I would prefer that no one panic sells. If no one does, the shorts will be left holding their (rather small) appendages in their hands.