There are a few reasons why your cat's nipples may be sticking out. One possibility is that your cat is in heat. When a female cat is in heat, her body releases hormones that cause her nipples to swell and become more prominent. Another possibility is that your cat is pregnant. During pregnancy, hormone levels fluctuate and can cause the breasts to swell and the nipples to protrude. If you notice any other changes in your cat's behavior or appearance, such as weight gain or loss, increased urination, or nesting behavior, it's best to take her to the vet for a check-up.