Cut a thin slice across the top of the end of each hot dog, making a nail bed.
Cut three shallow slices across the hot dogs in two places, to resemble knuckles. Break the other end off roughly, if you like.
Separate the onion wedge into layers and cut four pieces that resemble a fingernail.
Put about an inch of water in a medium saucepan and set it over medium-high heat.
Cook the hot dogs and onion pieces for about 5 minutes, until the hot dogs are heated through and the onion pieces are translucent.
Squirt some ketchup into each bun and tuck in a hot dog, placing a piece of onion over the nail bed.