I would have to disagree with the above statement. There are two known grunts in the game. One kind are with the covenant and the other is with the Heretic. If you look extremely close to the grunts on the covenant's side you can see that it has a penis. And if you look at the grunts for the Heretic's side you can see that they have a vagina. Also, i have a cousin that works for Bungie and he has informed me that, yes, there are two kinds of grunts.