Whenever my cats had kittens, they'd always eat their baby's poop if they made a mess on the floor. In this situation, it's instinct. In the wild, many females in the animal species ingest their babies' poo so that a predator doesn't smell it and come a sniffin'. I can't imagine why they'd do it under any other circumstances. They like the taste? My ex's pug loves to eat dust. The vet said it was probably because they could taste salt in the dust? YMMV.