Anthrax is a grey and white cat, owned by Annie Huit. She has grey-and-white fur and large green-brown eyes. The grey fur on the top of her head swoops down to form a peak on her forehead, while her face is white. The rest of her body is grey, except for her chest, stomach, right leg, the top half of her left leg, and the tip of her tail. Anthrax appears to have also gained Annie's power of exceptional intelligence, and according to Zinnia, has become more bossy towards the other cats, similar to how Annie began to take charge of the household after their parents went missing.