Oshawott has a scalchop on its chest. These are detachable, and are often thrown. They are used in the execution of the move Razor Shell when performed by a Pokémon with a scalchop.
Scalchops are made of the same material as fingernails, known as Keratin, and are capable of regrowing if they happen to get destroyed. According to a book in the Nacrene Gym, Oshawott's scalchop grows from its bellybutton.
Scalchops are shown to be vital to Oshawott, and its evolutionary family's survival, as it provides defensive and offensive benefits. According to Professor Oak's Live Caster, an Oshawott uses its scalchop to break open Berries, and only lets those it truly trusts touch it.
Scalchop Island lives not to far to the oshawotts, an island celebrating Oshawott and Dewott. The island is shaped like a scalchop and its inhabitants sell merchandise based on it, such as T-shirts and souvenirs, but also food wares shaped like scalchops.
If the scalchop is lost it can be NEVER be replaced.