Here's close to the final stage: Here the wound is made up of toilet paper glued to my arm, then the surrounding area was covered in white Halloween make up, then dirt. Then food colouring was added to the toilet paper. Then more dirt. I was a very dirty boy by the time my costume was done.
Here's the end result. A little brushing to make the dirt look a little more natural, a lot more fake blood and colouring. If you look closely the blood from the wounds twirl around my hand and off my pinky. I found it interesting to see how it flowed down my arm following the contours.
Here's a video of me in action: