I know you already found the answer, but I want to add that shark skin is only smooth in one direction, if at all. The scales are made of V-shaped grooves, like their teeth. Their skin can definitely break yours if rubbed in the wrong direction at a fast enough speed.

I can personally vouch for this. I used to volunteer at aquariums. The sharks and manta rays were my favorite exhibits to work in. Penguins were dope too, but they smell.