It's been about half of the first month since Bilbo started living in the Mountain, when he began to notice something strange. An unpleasant feeling, as if someone was watching him from the dark corners of long stone corridors. Sometimes he heard strange sounds like muttering or creepy and raspy laughter, but he knew that there was no one else in the Mountain except himself and Thorin. 

He thought he was starting to lose his mind, and was surprised when Thorin asked to come with him after Bilbo expressed his concerns to the king. Thorin led him to a rickety spiral staircase, that ended in a spacious room with makeshift roosts and nests, and a lot of very curious ravens.