Well...they appear to be mushrooms growing up from the carpet at the base of the bookcase.
Since "creepy" is what causes an unpleasant feeling of fear or unease, the negative health implications of such a thing is justification for the moniker.
I find that creepier than a pale, sunken-eyed woman in a tatty nightgown standing at the end of a dark hallway.
Edit: Then again, it could be referring to the presence of Mocking Jay, The Girl with the Dragon Tattoo and other banal works of fiction on the shelf.
Scary thought: What if the mushrooms are there because of the books?
Early radiologists would calibrate their X-ray machines by sliding a hand slowly through the beam in thirty second intervals. This photo (c.1900) shows the damage caused by radiation exposure
