Snatch and Swallow [Monstrous]

You can swallow creatures you have grabbed with your bite attack.

Prerequisites: Con 19, dragon, Snatch, Improved Snatch, size Huge or larger.

Benefit: If you begin your turn with an opponent held in your mouth, you can attempt a new grapple check (as though attempting to pin the opponent). If you succeed, your opponent takes bite damage and is swallowed. See Swallow Whole for details on how a creature might escape your stomach and the various consequences for that swallowed creature.

Swallowed creatures take damage in each round they remain swallowed, as shown below.

1. Maximum size of a swallowed creature. Your stomach can hold two such creatures; smaller foes count as one-quarter of a creature.
2. A swallowed foe takes bludgeoning damage in each round it spends in your stomach.
3. A swallowed foe takes energy damage in each round it spends in your stomach. The type of energy is the same as that of your breath weapon, unless the text of your creature description indicates otherwise. If for some reason you lack a breath weapon, the energy type is acid.

Source: Draconomicon, page 73. A certain amount of rewriting here was done to allow for the alternate rules under the Swallow Whole attack, which reduced the feat description considerably.