Two days ago, I adopted a brown and white kitten (two months old) and a black kitten (three months old) from the Animal Welfare League, a pretty well-known animal shelter. My question concerns the black kitten. When animals are adopted out, they have been through their first set of vaccinations and whatnot, and have been deemed as healthy. The black kitten is a month older than the brown/white, but is much smaller in weight. She has no problems with eating, and is a very active, playful kitten. I noticed today that her stool has a rancid smell to it, much worse than the other kittens. After doing some of my own research, it seems that worms are the cause of foul smelling stools in underweight cats. She has had the vaccs for worms, and was cleared to adopt out, so it couldn't possibly be worms. Could there be any other explanation for this?