Cutting A Key With Just Your Fingers

I guess at some stage, we've all had to have a key duplicated. Here's a unique method of duplicating a key without the use of a key-cutting machine.
The magician has a key examined by the audience. He now introduces a key-blank which can also be examined. With just his finger, he traces the outline of the key onto the blank. The blank now has the same contours of the original key, both of which can be examined yet again.