Not all of them.
Some are smooth skinned, some are sandpapery.
( Esme Weatherwax I swear on my tash it's daycent hash, Wed 3 Jun 2009, 10:45, archived)

That would be the smooth skined sharks.
Also, not all sharks have heads that are shaped like hammers, but they are shit at bashing in nails.
( turb0t, Wed 3 Jun 2009, 10:50, archived)