1. With a small paring knife, carefully cut off a small layer of the hot dog at the tip (this will be the area where the fingernail would be), and cut off the other end completely.
2. Right below the area where the fingernail will be, make 3 small cuts on an angle, then again in the opposite direction and again where the knuckle would be. Once the hot dogs boil, this will give them a more realistic look.
3. Do this step with each hot dog until all your fingers are made.
4. Cut the onion in half, and remove the 2 layers of onion skin.
5. Bring a large pot of water to a boil over high heat. Once the water is boiling, drop the onion pieces and the hot dogs into the pot. Boil for about 5 minutes, and then drain.
6. Using a knife, cut the onion into strips and then into small pieces that look like fingernails. (Try to keep them the same size as the hot dog so they look real and the onion fits properly.)
7. Add a few drops of ketchup on the hot dogs, then place the onion “nail” on top, creating the finger.
8. Once all your fingers are done, put them into hot dog buns, and place them on a serving platter.
9. Garnish with extra ketchup, and serve