Woochie Skin Flap is a latex prosthetic piece that can be used to simulate an open wound. Great for Halloween, or for theatrical and stage effects. 

You will need a glue such as Kryolan Spirit Gum. Apply it to the back of the Skin flap prosthetic anywhere it will touch the skin, and also to the skin itself. Wait for the adhesive to go tacky and then position the piece on the skin and press down to glue into place. The edges can be blended into the skin by stippling some liquid latex onto the edges of the prosthetic and the skin, using a stipple sponge. The edges and the skin can be painted up using a cream-based makeup, such as Graftobian Rubber Mask Grease.