The same reason Mogget is spying on a man who works in the same building as Samantha. But Cesare's bemused response is rather convincing. If he's lying, he's doing a good job.

The cat narrows his eyes. "You go if you wish. I've seen enough nauseating displays for today."

Witch, vampire, in the end it all comes down to the same thing. And to think that politics is decided on a whim of who can get into bed with whom. Humans never change.