I'm stumped. I've had cats for over 55 years but this is new behavior for me. We have two adult neutered male indoor cats. They are 5 y/o now, we've had them since they were kittens - litter mates. We have two cat boxes that are cleaned every evening (sometimes morning too). No changes to food, brand of litter, location of boxes, feeding schedule, etc. Fecal sample taken to vet - all clear. No other behavior or physical changes. For 3 days now, one time a night, he poos in the house, nowhere near the boxes. Based on trail cameras we know which cat it is and we confirmed that other times of the day he is using one of the cat boxes. I've tried blocking the favored spot, so he picked another nearby spot. Always poo, never pee. Not sure what to do at this point - anyone have ideas?