I have four cats. two kittens, the mother and the mother's sister which has never been pregnant, but we didn't spay her. The mother hisses at her 9 week old kittens and doesn't nurse them, so they have been suckling on the nipples of the other cat and she lets them and grooms them. Can she produce milk or are they just suckling for comfort? i can see a liquid on the nipples but not the color because of her white fur.