Sorry for the late reply. Anyway, <Digest: 100> is not going to do anyway, it should be <DigestHP: 100>. However, what you may be looking for is <DigestHP: -100> where -100 takes away 100 HP from the prey.
Also, I just read through and noticed that the popup doesn't appear for digestion. A quick look shows that the processes for setupDamagePopup are different, so I'll have to rewrite that part.
The fix for this and the "cannot save" should be up in some time.