You move your hand to pet one of the cats, but as you stroke its back, your hand goes right through it, just like all ghosts in ghost stories. But as you pet the cat, it gives a purr, and your hand grows chilly like ice. The other cats, seeing your affection, mew and make their way towards you as well, expecting a lovely carress. You provide these for each of the exultant ghost cats, but at the same time, you count them. Looking back towards the shelf, you count the number of skulls sitting in the bookcase, and find the number to be the same. Apparently their feline souls are confined to this house where their skulls are kept. Either that, or they want to stay.
Leave the house 
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