My dark friend

In the winter, when the sunbeams are long into the window, I have this pal that follows me around. It is this dark cat that doesn't speak, isn't furry, and does what I do. I sit, dark cat sits. I sleep, dark cat sleeps. I jump, dark cat jumps. Then when the sun goes down, and it is time for dinner, dark cat leaves. I am so glad I do not have to share my dinner with dark cat.