Kudzu v. Grape

Okay, how do I identify the difference? Mr. Google seemed singularly unhelpful, as did our local ag extension service. I've got some vines that are grape, some that are kudzu (we're selling that house), and some that are unknown (the grapes made themselves known by giving fruit, the kudzu by not giving fruit for four years, the unknowns we haven't had that long). Having grown up in and around the Blue Ridge Mountains, I know what that little booger kudzu can do, and I want no part of it. But I don't know how to tell the difference.