You have to depress the fingernail edge slightly (where the flesh almost starts). A little like a mouse click. But the finger is not touching from close observation.

lol, I am aware it is not the finger nail per se. Its just being used as a regular and consistent reference point (if you always use the same point) to transmit the capacitance from your finger as you press the nail in. That's probably what gives it its accuracy.

Anyway, I wouldn't be so stupid to suggest something that is easily non-reproducible and easily debunked with common objects. And I am sure what I am doing can be easily explained, but all I know is that it works using the stipulations set.