Why is my 12-week-old kitten refusing to use the litter box?

There could be several reasons why your 12-week-old kitten is refusing to use the litter box. It could be due to stress, a dirty litter box, a medical issue, or a preference for a different type of litter. It's important to consult with a veterinarian to rule out any medical issues and to try different litter box setups to see what works best for your kitten.