Lily-livered

I have talked about the expression "lily-livered" before, but when it was featured this week by Merriam-Webster's Word of the Day, I thought it worth mentioning again. Here is what Merriam-Webster has to say about lily-livered:

"lily-livered  \LILL-ee-LIV-erd\  adjective
: lacking courage : cowardly

Example sentence:
"I regret not hurling myself into university life because I was too...lily-livered to live a little." (Laura Barton, The Guardian [London], August 16, 2001)

Did you know?
The basis of the word "lily-livered" lies in an old belief. Years ago, people thought that health and temperament were the products of a balance or imbalance of four bodily fluids, or humors: blood, phlegm, black bile, and yellow bile. It was believed that a deficiency of yellow bile, or choler, the humor that governed anger, spirit, and courage, would leave a person's liver colorless or white. Someone with this deficiency, and so white-livered, would be spiritless and a coward. "Lily-livered" and "white-livered" have been used synonymously since the 16th century, but "lily-livered" is now the more common expression, probably because of its alliteration."

What's so funny about this? Bile is a bodily humor. (I can hear the groans already.)