I noticed something in the Slavering Maw's tactics section. I thought the zombie-spawning thing was the various stitched-together zombie parts tearing themselves free. But in the last sentence of the tactics section says the Charnel zombies it creates when it dies are its most recent meals!
Which makes me think "Wait, why aren't the most recent meals clawing at the PC in the thing's gut? And would close attacks not wound them?" Of course, attacking the minions in the gut wouldn't be very fun.
I also wonder how many creatures the thing can swallow. It doesn't say.
Sidenote: I wouldn't spring a mad wraith, or really, any wraiths - on a party without SOMEONE who could do radiant damage. That's just cruel.