Even through her tears, her puzzlement was plain. He probably thought nobody else was smart enough to get it. Bilirubin is a primary component of bile. She snorted, but was still too upset to giggle, so I went on. It has special relevance here.
All bilirubin is, really, is red blood cells that died and decomposed.
Dark brown goo. The liver skims it out of the blood, and passes on the intestines for disposal. I gave up and held her. She would tell the rest of it when she was ready. And I couldn't see any angle of approach.