SRD:Rake

Rake (Ex)
A creature with this special attack gains extra natural attacks when it grapples its foe. Normally, a monster can attack with only one of its natural weapons while grappling, but a monster with the rake ability usually gains two additional claw attacks that it can use only against a grappled foe. Rake attacks are not subject to the usual –4 penalty for attacking with a natural weapon in a grapple.

A monster with the rake ability must begin its turn grappling to use its rake—it can’t begin a grapple and rake in the same turn.