I've seen so many parasites and parasite parts coming out that my first reaction this weekend was "Oh my god, that one is really big and really weird!" And there are some many!
It was a mushroom slice. Lots of mushroom slices, evidently, that I had not digested properly.
Made me pause and think: Does my parasite medicine recognize the mushroom as a fungus and attacked and killed it? I have no other explanation for why I didn't digest mushrooms from my homemade pizza this weekend.