The idea is that you insert the sharp point into the seam of a walnut – just in the back where it actually grows from the tree (the flat part).
I have to note this find here as proof that walnut keys do exist and that they are NOT something I just made up. Years and years ago, I came across a walnut key that a jeweler had made and thought it was a fantastic idea, not to mention beautiful. Since then I’ve been kicking myself for not buying it then and there because THEY ARE IMPOSSIBLE TO FIND. Also, when you ask people if they have ever seen one they look at you like you’re just nuts.