The principal behind the psychic damage thing is explained in the introduction: personal taste. I'm not into digestion, but I know others are. Optional rules are included at the end of the document to substitute in and it can be done with no other adjustments. I was using the psychic damage to simulate a feeding on the mind/soul rather than on the body. The damage stops when the creature within is rendered unconscious.<br/><br/>While I do understand the ability to climb out of a larger predator, it shouldn't be practical for one closer in size. I had initially skipped the action to attempt to climb out as I was trying to avoid unnecessary rules clutter, but I could easily add it in under the optional rules for people who want to use it in their games. Something like "if you've been swallowed by a creature at least X (1 or 2?) size categories larger than yourself, you can use your action to attempt a Strength (Athletics) or Dexterity (Acrobatics) check contested by the creature's Strength (Athletics) check. Success removes the swallowed condition and returns you to the creature's mouth with the ingested condition."<br/><br/>As for the grappling rules in 5th, if one of my players argued that they wanted to try to grapple something that the rules say is impossible, I would allow them to try it with disadvantage. If they had rope or some other brilliant plan, I would remove the disadvantage and maybe even give them advantage if their idea was really brilliant. Just giving the check disadvantage will, in most scenarios, make it very unlikely they would succeed, but that is better than impossible while maintaining some realism.<br/><br/>I was worried that the feats were too powerful, but, like you said, I decided that they were powerful feats built around a system that isn't terribly powerful. If the game is using the standard rules for when character's get feats then I think it is probably fine.<br/><br/>I had included a line in the "Rules for Escaping Your Stomach" section of "Rules for Predators" that specified the attack needed to be a light piercing or slashing weapon, but I do agree that that should be given additional visibility. I'll add a line limiting attack rolls to such weapons into the Swallowed condition. Should it also be added to the ingested condition, too?<br/><br/>I thank you again for your feedback! It's been a pretty big task to tackle.