Toby is Molly Hooper's cat. She bought him on 2 February. At first she wanted to name him after Sherlock, but she thought he was too "cute and fluffy", so the name did not fit. Toby is mentioned on Molly's blog where she also posts a picture of him. Her blog is the only place we hear about him, he is never seen or mentioned on screen in Sherlock. In her blog she explained her intention to buy a cat with this: