Bella's first response is to apply logic: if Sherlock is asleep and thus cannot hear or see his surroundings, and the entity's only weapon is appearance and words, then it cannot have any effect on him while he sleeps and so there is nothing to fear.

The problem with that, however, is that if logic worked to dispel phobic reactions, then phobias wouldn't exist.

She thinks, then tries a different approach.

"It taught you something new about yourself," she says. "It's best to know about that weakness before it's exploited by something that can do you physical harm."