Subject A knows all of Subject B's scars. He can list them in all sorts of ways. Top (wax bottle smashed on head) to toe (nibbled by duck). Largest (mantrap) to smallest (zit). Oldest (hit in the face with a red plastic block as a toddler) to newest (line of punctures from a fish's fin). Funniest (champagne bottle) to most harrowing (another candidate for smallest, this- but it's on the face, and it was his fault, he forgot to take the custard pie out of the tin, and he hasn't forgiven himself).
There's one scar, though, a small line on the back of his left hand, that Subject B won't talk about. He just says he got it in training and smiles slightly.
Subject A knows that stumbling into a roomful of mousetraps would be a funny thing to demonstrate. He is ready; he found one a long time ago and now it is sharp. When it swoops down it will make a perfect red moon, an elegant sweeping curve, and the bite will leave nothing of the old mark behind.