Check the Great Big Table podcast (http://greatbigtable.com), a podcast about expanding the board game hobby.
Nope, it is a free action. Making it an action sounds like a deliciously cruel variant, though.
That's how we've been playing and it seems to work. It makes going after each other worthwhile even after all your opponent's teeth have been knocked out.
We'll have to try it the real way to see how that feels.