I originally saw this idea on a blog called Desserts by Candy. You can find the entire from-scratch cake recipe there.
Her cake and fingers are much more beautiful than mine (which is pictured here). She had the fingers sticking straight up from the top of the cake. Since I rarely bake from scratch (I'm a cooker, not a baker), I used a brownie mix recipe. My interest in her post is how she does the fingers. So here are her instructions with my images.
"To make the fingers, shape the marzipan into five logs of vary length and score lines with a knife to make knuckles. If the marzipan is too sticky to work with, dust some icing sugar on your palm. Press a sliced almond to one end to make the finger tip and adhere with some left over chocolate glaze. Adhere the finger to the cake with more left over chocolate glaze and prop them up with toothpicks if necessary. Sprinkle some chocolate cookie crumbs around the fingers to make dirt."
Just for reference, she used 100g of marzipan. If you don't like marzipan, you could create the fingers using fondant.
I was pretty pleased with how it turned out. I used a simple butter knife to score wrinkles and the outline of the nail into the fingers.
If you want your cake to be more colourful, consider creating grass around the mound of dirt and on the sides of the cake. Use vanilla icing and add a few drops of green food colouring before applying it.
I decided to use red food colouring to make the nails appear bloody. And instead of using ground up cookies for the dirt patch where the fingers "rise up", I just minced up the brownies on one side.
Marzipan is pliable, so it was easy to bend the fingers at the knuckles to make them look more life-like.
I used some of the ground-up brownies to cover the ends and voila.