11 yr old son (vegan), stool is rancid, smells like something died. he said his stool is normal in color and consistancy. what can cause this?

Foul odor: Eggs might possibly be the culprit.Hard boiled eggs may produce foul smelling gas.

Incomplete digestion: Sometimes, food is passed from the small to large intestine without being completely digested; the bacteria in the large bowel then work on the incompletely digested food, causing foul odors and sometimes gas. Sugars can be a major culprit. This is very common after episodes of viral stomach flu; the virus causes lower levels of enzymes in the small bowel, which will return to normal in a few wk.