My 15 year old cat, who has arthritis, has stopped burying her poop in the litterbox. Shes had arthritis for a few years and she's always buried her poop but has stopped doing so for a couple of months now. Nothing in her environment has changed, that I'm aware of. We have two other cats who she doesnt care for, but they've been with us for fifteen years as well. Do you know why a cat would stop burying--could it be related to her arthritis, is it something psychological, etc? How can I get her to start burying again?...it stinks!