Is that what passes for dancing these days?

So we were all out at the Rue Bar tonight, livin' it up, dancin' it up, you know the deal. Now, I should say that I don't usually do that sort of thing. Nevertheless, as I found myself sandwiched between two voluptuous women, our hips gyrating in rhythmic unity, I couldn't help but wonder if it's "ground" or "grinded." I mean, obviously, you say "the pepper was ground," but since "to grind (against someone)" is a derived construction, does it follow the same pattern? Anyway, I think I lost the rhythm somewhere in that thought. After all, it's sorta hard to stay focused while grinding.