It's a fantasy role-playing game.

DM: You are Vax Vax'ildan, a half-elf rogue . You are the member of the famous group of adventurers. Previously, Tiny you, thanks to a potion that does that. Scanlan managed to go ahead and put in an Immovable Rod within its stomach, which held it up for a moment, before it decided to truly gain the advantage it needed to escape the circumstance, allowed it to tear through its body, as well as an arrow that was shot by Vex, towards her brother, in the hopes of, I don't know, being a symbol of hope?
DM: Yeah. Okay, so, the blade is in there and it has found its way through the existing wound, but you don't quite have the strength to actually wrench it enough to do any real, serious damage as it is a very, very hardy and well-defended creature from its natural mass. The fleshy interior of a dragon is almost as dense and as protected as the armored hide on the outside, and that's one thing you weren't counting on when entering its form.
Player: And what did I just do, though, with the dragon sword, did I widen the hole?
DM: You've put the blade through the hole and so now you have that blade lodged in, you can then use that to try and widen it in successive turns in itself and that will prevent you from having disadvantage on the attacks with that blade going forward, because it's already in a soft place and you can just wedge it, but it's going to be a strength attack for each of those rounds. The dagger unfortunately, you just can't find any purchase at that point there in the time given, because of the movement and the squishing. You do also suffer an additional seven points of crushing damage.
Player: Okay, and I forgot. One other thing I want to do-- I have movement too, can I use my legs to push as hard as I can forward a foot or something? I know with movement over difficult terrain it's halved, and I'm in the most difficult terrain.
DM: You are in the most difficult terrain there probably is.
Player: But if I use my movement could I shove and go like a foot towards the outside, half a foot or anything?
DM: Pushing towards the wound?
Player: Pushing in. Using my legs to go--
DM: Okay. I would say that would be part of your attack next round. Actual movement within, you would be able to move a few feet but you'd have to release the blade to do so. Any actual blade pushing forward would be your next action, so hold off for the next round. Scanlan, what you got?
