When I lived in the Keys I did a bit of work for a dive shop and because of that I could go out on their boats whenever I wanted. An instructor there called and asked if I'd go out with them and help out with extra divers. On the way out I am suiting up and these two brothers, both in their teens see me strapping a knife to my leg and I have another on my leg.
One brother ask me what the knives are for and I reply
"Oh, those are for sharks"
What? Huh? Sharks? The other asks if he can see one, so I pull my work knife off my leg, it has a blunt tip. Kid says
"You said this was for sharks, you can't stab a shark with this."
I reply
"Feel the blade, I don't need to stab a shark, I just slash your leg and swim the other way"

Two kids, big saucer like eyes!
My buddy Bill
"Thanks Stan, this should be interesting"