It's common sense vs. game rules! Let's say you're inside of a behir:
>>> AC 21, 7 natural attacks, swallow whole (2d8+9 bludgeoning damage, AC 16, 10 hp)
It's arguably safer on the inside. However, I'm wondering whether you can defeat the beast like that. Its gizzard has AC 16 and 10 hp, but does reducing those gizzard hp to 0 actually reduce its pool of 105 total hp, or is it a separate pool? Once the gizzard is at 0, does additional damage actually hurt the monster?
I ask because it seems easier to get swallowed and smack the easier-to-damage AC from the inside until the beast falls over. Is this the intended interaction?
Here are the Swallow Whole rules for ease of reference:
If a creature with this special attack begins its turn with an opponent grappled in its mouth (see Grab), it can attempt a new combat maneuver check (as though attempting to pin the opponent). If it succeeds, it swallows its prey, and the opponent takes bite damage. Unless otherwise noted, the opponent can be up to one size category Smaller than the swallowing creature. Being swallowed causes a creature to take damage each round. The amount and type of damage varies and is given in the creature’s statistics. A swallowed creature keeps the grappled condition, while the creature that did the swallowing does not. A swallowed creature can try to cut its way free with any light slashing or piercing weapon (the amount of cutting damage required to get free is equal to 1/10 the creature’s total hit points), or it can just try to escape the grapple. The Armor Class of the interior of a creature that swallows whole is normally 10 + 1/2 its natural armor bonus, with no modifiers for size or Dexterity. If a swallowed creature cuts its way out, the swallowing creature cannot use swallow whole again until the damage is healed. If the swallowed creature escapes the grapple, success puts it back in the attacker’s mouth, where it may be bitten or swallowed again.
Format: swallow whole (5d6 acid damage, AC 15, 18 hp); Location: Special Attacks.