Thanks for your reply. The question is 3 years old but since I asked till now we haven't done it since we ae both not very sure about the risks involved.
There are two scenarios we read about in the first scenario the sub girl was required to lay down naked in the nettles and was required to move in them like making a snowangel. The second one was them being used as a kind of hitting instrument eventually on the pussy and bum and even inserted into them.
This last part about the pussy and bum is for both us a bit to far since we do not know what it does to the kind of tissue inside your pussy or bum. We only consider using it on normal skin back, belly, outside of the legs those kind of areas and maybe on the breasts.