[Sebastian's long-term planning capacities are flawless right now, shush.]
Eating is one of the things I enjoy. [Obviously? He's a demon, after all. And eating, by definition, involves murdering people. So hah.]
My master is not present, so there is no good reason to stay in the form I serve him in until we are reunited.
[In fact, it's incomprehensible why he's felt so particular about continuing to play the butler part all this time since Ciel left. All that effort when there's not even a Contract to show for it? He can easily just take on a new form whenever it's convenient to.]