Reasons for a cat's sudden change in temperament and its aggressive biting
1. The cat may be in heat. The anxiety and restlessness caused by heat can drastically change its temperament, making it aggressive.
2. The cat is experiencing severe pain, which is why it appears fierce and doesn't want anyone to approach.
3. Mother cat protecting her kittens. It's possible that she senses her kittens are in danger, which causes a drastic change in her temperament.
4. The cat may have rabies. This can also cause a drastic change in temperament and biting.
5. It's possible that when petting the cat, there's a lack of familiarity, causing the cat to have an instinctive rejection reaction. 
What to do if your cat suddenly changes its temperament and bites aggressively?
1. It is recommended that owners have their cats spayed or neutered after they go into heat if they do not intend to breed them.
2. If your cat becomes agitated and bites after being touched in a certain area, take it to a veterinary hospital for examination and treatment as soon as possible.
3. If it is rabies, it is recommended that the owner contact and report to the relevant authorities as soon as possible after diagnosis.
