Harry had let himself get bullied into being the Council's errand boy again, so they were keeping a thaumaturgist's magic mirror in the apartment until it could give evidence at his trial.
Bob had seen this sort of omniscient, cannot-lie mirror before. Owning one always ended badly. It was like reading minds: just too tempting to resist, but you never liked what you heard. That way lay madness. In his day, Snow White had been a sorceror's cautionary tale.
Bob liked to think he was too clever to fall into that sort of trap, but at night while Harry was sleeping and there was nothing to do, he found himself gravitating towards it. Surely it couldn't hurt to ask...but it could hurt. It would hurt, because he knew the answer wouldn't be what he wanted, and yet he had to know...
He resisted for two nights, but on the third he straightened, gave the mirror his most commanding stare, and asked, "Mirror, mirror on the wall, who does Harry Dresden love most of all?" (Rhyming was considered a show of respect in the magic mirror community.)
The mirror opened sleepy eyes and said, "Oh, an evil queen, my favorite type."
"Answer the damn question," Bob said through gritted teeth.
"Well, I'm not precisely on a wall now, am I?" the mirror asked. "No, I'm more shoved in a corner, if you catch my drift."
"Mirror," Bob said warningly. "You have a geas just as I do, and I asked you a question."
"Oh, all right," the mirror said ungraciously. "You, of course."