Has anyone tried willow withies? I mean branches, of course. Very thin (unless you use several in a bundle) and whippy. They CAN cut, but probably not, especially if care is used, or if used in a bundle, but they can FEEL like they're cutting you. It's a kind of sharp pain, but doesn't go deep and (shouldn't) keep hurting beyond a few days. Not much bruising, but they can welt easily. Other branches can have a similar effect, but tend to dry out quickly (and snap).