Re: Can Stress Cause Change in Poo Smell?
If the parkinglot kitten wasn't cleared by a vet prior to being introduced to the home, it is possible he was carring something that the other kitten now has.
Particularly stinky poo in both cats and people is usually an indication that something unusual is going on in the digestive bits-n-pieces.
If the stool is well-formed (not loose or runny) I personally might wait a day or two to see if it cleared up. If it's runny or very loose, I'd be getting the kittehs to the vet pretty soon, cuz little ones can go downhill pretty quickly.