yeah, this is what sharkskin looks like under a microscope:
it’s covered with tiny interlocking teeth that form a one-way-only surface! petting a shark the wrong way will literally make you bleed, which is still never a thing you want to do if you are in the water with a shark.
(yes, those are literally teeth-sharks ended up evolving a skin covering completely separate from the scales that bony fish ran with and they did it by mutating the teeth out of their fucking mouths and over their entire surface area)
