Tummy Sticks -- Even I Don't Know

Can someone out there tell me what it means to "play tummy sticks?"

Yes, I saw "Wedding Crashers." And, yes, I've been thinking about it a lot (granted, not too much, but still...), and even my corrupt and pervy mind can't think of a concrete definition. Instinct tells me it has to do with a *ahem* stick that, er, rises to hit one's tummy (in plain language, I think it has to do with erections), but can anyone confirm this? What's the exact definition? Is this its first use? What's the etymological origin, even??? :)

I'm going crazy with this gap in my mental dictionary of depravity!