Black-green and smelly stools are related to indigestion, imbalance of intestinal flora, gastrointestinal bleeding, etc. When indigestion occurs, food is expelled from the body in a semi-digested state, and the bilirubin in the stool is not oxidized by alkaline substances but oxidized to bilirubin in an acidic environment, resulting in black-green stools. In the case of indigestion, the stool contains a lot of undigested food and therefore has a sour odor. When Pseudomonas aeruginosa is overgrown in the intestinal tract, it reacts with food residues and produces a foul odor, and the color of the feces is green. When there is bleeding in the digestive tract, some blood is excreted through the digestive tract and oxidized by the digestive tract, resulting in black stools with a foul odor and, in some cases, tarry stools.