Robert Neamtiu brings us a handy instructable on creating wounds using latex and tissue paper. The tutorial uses makeup-grade liquid latex, but I would humbly suggest saving yourself a pile of money by using Capitol brand #017 Latex Seam Sealer instead. It's exactly the same thing. No, strike that. It's actually a better product since it includes a higher proportion of latex solids. I buy mine at Lowe's, but you should be able to find it at any big box home improvement store.