Dumbledore had tried using a drop of blood that he had taken, but it had gotten him nowhere. The seal hadn’t budged. So it was not blood magic after all, only familial magic. As he poured through several mundane memories of Morfin gaunt, he kept coming up on the one where he confessed to murder. There were some more lewd memories and he had never thought to watch them before, but now that Ms. Granger was in play, he needed to know all the women Morfin Gaunt had "been with’. He was going through one memory after the next, taking notes of the names.That was how Minerva found him in the pensive "Dumbledore!! What on earth?"