Great question about the dolphin's belly... pretty smooth I'm guessing, because they're mammals, but funnily enough I read somewhere (was it Hawaii-5-0 fanfic?) that sharks actually have not only a rather rough hide, they (some of them?) have denticles, like skincells that are shaped like teeth. For streaming purposes? I'm not sure of anything anymore but I ust have to obnoxiously infodump...