Harry gave Dumbledore a description of the dream he remembered having of Voldemort and Wormtail in Little Hangleton, of their "plans’ that Harry overheard them mention but didn’t know what. Dumbledore was attentive, but just as Harry was finishing his tale, he felt something in the back of his mind. It was foreign, not supposed to be there and it was trying to get in by probing at his surface thoughts. Harry was shocked. What was this?