Possible reasons for hissing:
* Territoriality: Even though they're neutered/spayed, cats can still be territorial. Maybe Roberto feels that Della is intruding on his space or resources.
* Resource guarding: This is similar to territoriality but focuses on specific items like food, water, or favorite toys. If Della is approaching something Roberto considers his, he may hiss to warn her away.
* Stress: Stress can cause cats to become more reactive, even to other cats they usually get along with. Could there be something stressful in the environment?
* Personality differences: Some cats are just naturally more shy or cautious than others. Maybe Roberto is just a grumpy cat who doesn't like to be bothered, even by Della.
* Medical issues: While less likely, health problems can sometimes cause aggression in cats. If the hissing is new or accompanied by other changes in behavior, a vet visit is warranted.
How to help:
1. Observe: Pay close attention to the situation leading up to the hissing. What triggers it? This can help you identify the underlying cause.
2. Separate: If the hissing is frequent and intense, consider giving them separate spaces, especially when feeding or using the litter box.
3. Gradual introduction: If they haven't been properly introduced, try doing so slowly and calmly, starting with supervised interactions in neutral areas.
4. Enrichment: Give them plenty of stimulating toys, scratching posts, and climbing opportunities to help them channel their energy and reduce boredom.
5. Consult a veterinarian: If the hissing persists or you are concerned about their behavior, consult a veterinarian. They can rule out any medical issues and offer advice tailored to your specific situation.
It's important to remember that cats communicate differently than humans, and hissing can be a warning signal, not necessarily an act of aggression. By understanding the possible reasons behind the hissing and addressing them, you can hopefully help your cats develop a more peaceful coexistence.