sorry if this has come up but i couldn't find anything :Z, so basically i just want to be sure my logic is correct .. you have a foe , my eidolon grapples and swallows great, so now the enemy is in my eidolons belly as lunch ,
now if i were to cast caustic blood on my eidolon and then the said foe were to try and cut or claw its way out causing it to get a face full of acid dont matter if it cuts it way out or not, would it still get a reflex save to negate considering theirs no way for it to dodge as its basically trapped inside the snakes stomach? i know they have the grappled condition while swallowed but a reflex save against what would be a 10ft spray of acid while inside the tight confines of the stomach?
RAW, yes unless your DM says otherwise. The rules say the DM may waive a save under certain conditions, but reflex is as much luck as it is actual moving, hence why sleeping characters can still make reflex saves.