Determining a kitten's age:
1. Umbilical cord. If you see a kitten whose umbilical cord hasn't fallen off yet, it's probably no more than three days old.
2. Eyes. Generally speaking, kittens open their eyes around 10 days old; this is an average figure.
3. Ears. When a baby is born, the ear canal is closed. It begins to open around the 5th to 8th day and can stand up around the 15th to 20th day.
4. Teeth. The general order of tooth eruption is: incisors (10-15 days), canines (15-25 days), molars (30-40 days). 
The growth stages of a cat:
1. Newborn kittens refer to kittens that have just been born. They are very delicate and need to be cared for in all their daily activities. They are unable to take care of themselves.
2. Kitten stage, referring to the period from birth to weaning. At this time, the kitten will open its eyes to see the world, be curious about everything, and must rely on its mother or humans for care.
3. Kitten stage, referring to the period from weaning to about one year old. This is the most curious and active period in a cat's life, during which it learns all the skills and lifestyle habits of cats.
4. Adult cat stage, referring to cats aged one to ten years. This stage is the longest and the most important stage of a cat's life, during which they complete their reproductive tasks and all daily chores. Cats at this age are most alert and perceptive of their surroundings.
5. Senior cat stage, referring to cats over 10 years old. At this stage, the cat's physical functions decline, it is no longer active and needs careful care from its owner.
