"A strange thing hangs by a man's thigh, hidden by a garment.
It has a hole in its head. It is stiff and strong and its firm bearing reaps a reward.
When the man hitches his clothing high above his knee, he wants the head of that hanging thing to poke the old hole (of fitting length) it has often filled before."
Source: A History of Western Society by McKay and Scott.
A key?
Well done!
Heartbeats fluctuate on multiple levels based on multiple variables. However, they generally keep a steady rhythm. More than this, though: in cases where the lack of a heartbeat defines death, the presence of a heartbeat will define life. That's an important and precise dividing line for people who like to keep breathing.
In any case, I think you should sue your dentist for malpractice.
(Name's Bond. James Bond)
It's a grill. I'm trying to draw attention away from the bump on my forehead. It seems to be working, too.
@LoekBergman: I like the riddle, btw!