Shorts sell shares they don't own in hopes of the pps going down. If the pps goes down they buy what the shares that they didn't have at a lower price. Their profit is the difference.

If anything causes the pps to start going up and lots of shares are out a stampede can occur....short squeeze..and the pps can rise fast. The more short shares to cover the worse the squeeze.

If the data shown is correct a kit approval could cause a squeeze.