Technically, "rear" isn't a "rear kick" so much as "rearing up to
kick", unlike assassin's mule kick which is a directionally backward
kick. Per helpfile -

> While fighting, a centaur can forgo a round of melee attacks to rear up and
> strike out at their opponent with their forehooves. This tiring assault is
> typically more effective for centaurs with more martial training.

Not that it invalidates Scarabaeus's comments, but I had to correct
myself of that imagery as well. Which then leads to my question...
when a centaur kicks, is *THAT* a directionally-backwards kick like
horses? Or is it just lashing out with a single hoof? *fistshake*
I blame Scarabaeus.