Green discharge from swallowtail cats

Two of my cats have been discharging fluid and eaten plant. cant tell which end its coming out of. both are appearing to be healthy otherwise. Is this normal? Both are in a tank eating flat leaf parsley.

Karen says:
Yes this is normal. Monarch caterpillars do not do this and I wondered as you did if something was wrong, but my experience is that it is normal with the black swallowtail caterpillars.