. Along this same vein
The Straight Dope comments that the colour yellow has long been associated with cowardice -- in France, the doors of traitors' houses were daubed with yellow, a medieval yellow star (continued by the Nazis) branded Jews as having "betrayed Jesus." They continue, saying that in the North American Western frontier in the 1800s, a "yellow-dog" was anything worthless.
"That yellow-bellied, snake-blooded, skunk-eyed, rancid son of a
parallelogram!" she said. "This time he picked the wrong grandma." Little Red Cowboy Hat
by Susan Lowell.
Marty must rescue the good doctor, however, when he learns that
the treacherous Mad Dog Tannen, leader of the rascally Tannen gang, is gunning
for Doc -- and the yellow-bellied coward won't hesitate to shoot him in the back.
Excerpt from the Back to the Future III liner notes.
Several creatures are literally yellow-bellied