As is the case with other sharks, the skin of the shortfin mako is covered with tiny scales known as denticles. These are angled back from the front of the fish, so the skin feels smooth if you run your hand along it from nose to tail, but rough if you go "against the grain" in the other direction.
Led by astronautical engineer Amy Lang, a team from the University of Alabama discovered that on key parts of the shortfin mako, those 0.2-mm-long scales (pictured below) are capable of flexing up to an angle of 40 degrees out from the body. They do so in response to reverse water flow, which occurs due to a phenomenon known as flow separation.
In a nutshell, flow separation happens when fluid passes around the front of an object that's travelling through a liquid environment (or that's held in moving liquid), forming eddies alongside its back end. Those eddies create drag, slowing the object down – this effect can hamper both watercraft and aircraft, as it also occurs in the air.