With the way the [Polymorph] spell is worded, a creature reverts back to their normal form if their morphed form is killed. During part of the campaign, a creature had been polymorphed into a small animal and then fed to one of their allies. Eating the polymorphed creature caused it to be killed and revert back to normal form inside of the other creature; which then caused the eating creature to explode/be ripped apart. This has opened up talk of other ideas such as the party using polymorph on themselves and crawling inside of a foe for insta-kills. I'd be interested to get outside opinions on this situation.
DM could house rule that a killed creature doesn't revert back to normal form, or reverts back to normal form after 48 hours (or 1d6 days, or 1 month, or whatever)... It makes the idea less appealing if the target of polymorph gets digested before reverting back to normal form.