It's a fantasy role-playing game.

DM: You are Vex Vex'ahlia, a half-elf ranger . You are the member of the famous group of adventurers. Previously, Die! Die! .
DM: All right. Good to know. And so as you pull back the arrow and release it, there is that-- the way that you constructed it, there's just this pouch of very thick gooey-- is this the spell or is it the actual arrow constructed by Percy?
Player: It's the arrow.
DM: Right, the one that he built? So what happens is that the front of the arrow, it doesn't do any actual damage on the impact. Instead what it does is it, when it smacks into it, there's a pouch in the front that detonates from the impact and sends this very quick-setting tar, like glue substance. That just spatters across the body and lower torso, it expands like a foam. There's no damage on that one, but it's currently (grunts) grappled by it and cannot move from its place.
Player: Awesome. And so I'll shoot another arrow at the other lady.
DM: Okay. Go for it. Roll for an attack.
Player: I know she's running away, but she's a bad guy. I didn't hit her, though.
DM: What did you roll?
Player: 16.
DM: Heh. It's funny-- mages don't have a lot of armor. Even with mage armor, you manage to hit her square in the back. Go ahead and roll damage.
Player: 16.
DM: She goes (cries out) and stumbles, and catches herself and gets back up and you can see the arrow sticking straight up out of her back. Probably four inches into the back of her shoulder blade.
