The stab is a time-honored and interesting special effect in horror films, war movies and westerns. You have seen a machete protruding from Kevin Bacon’s chest in “Friday the 13th,” an arrow from Clint Eastwood’s shoulder in “Two Mules for Sister Sara,” and from Richard Kiel’s chest in “Force Ten from Navarone.” Quality companies like CinemaFX offer stab kits, but you can achieve a very convincing stab effect with some low-cost materials from a costume shop.
Collect specialized materials from a theatrical supply store, joke shop and so forth. The items that you will require, which are not readily available elsewhere, include theatrical molding putty (sometimes called “nose putty”); a realistic-looking but all-plastic knife; makeup that matches your flesh; fake blood; and Spirit Gum adhesive.
Rub a generous amount of molding putty between your palms, to soften it. Lay it on your glass or mirror, and spread it so that it forms a ridge in the center.
Cut off the plastic knife, near the handle (within 1 inch). Alternatively, cut off the blade point, with 1 to 3 inches of blade point; this will create the effect that you were stabbed from behind.
Press the cut-off end of the blade into the ridge in the putty. Build just enough putty around the blade such that it stands up without holding it.
Make up your appliance, with cream-based, flesh-colored makeup. Apply the makeup only to the visible surface of the putty. Paint around the edges of the “wound” with fake blood. You should now have a convincing appliance.
Cut a piece of gauze that is 1 inch larger on all sides than the base of your appliance. The gauze should have roughly the same shape.
Lift the appliance from the glass, using a putty knife or a razor blade. Transfer it to the gauze, and press down with the putty knife to press the putty into the gauze.
Dab your flesh with Spirit Gum, where you wish to affix the appliance. Dab the gauze side of the appliance as well. Allow 15 seconds for the Spirit Gum to become tacky. Press the appliance onto your flesh, and smooth out the gauze with your putty knife. Allow a few minutes for the Spirit Gum to dry.
Cover the exposed gauze with a thin layer of putty. Twist it between your fingers or your palms to soften it, and it should spread easily.
Make up the fresh putty and blend it to your flesh. Add a drip of blood, from the bottom of the blade downward.
These materials (including nose putty) are not "state of the art" for films, but they are the materials that Lon Chaney Sr. used in "The Phantom of the Opera" and which turned Boris Karloff into The Frankenstein Monster; they are easy to use, and very effective.
Use only cream-based or liquid makeup. The pancake makeup, which requires a wet sponge to apply, will not adhere to nose putty.
Stab wounds form “lips,” flaps of flesh that surround the blade. The lips you form with the putty will hold the blade steady.
Do not attempt this effect with a metal knife; it will be too heavy for these materials.
An easy alternative to the above (one commonly used in early Hollywood); tape a piece of Styrofoam to your flesh, with surgical tape. Put on a shirt or jacket, and cut a slit above the Styrofoam. Press the cut-off knife into the foam, and paint blood around it.