A hairbrush. Its intended purpose is mundane, basic enough that even a child can grasp its perfunctory mechanics. It is common. Expected. Easily dismissed. But, as with so much in life, things are never quite what they appear.
Hermione places an anonymous personal ad in The Daily Prophet. Snape is looking for a new lease on life. Will they be what the other needs, or will the past be too much for them to overcome?