So Dorcas knows nothing about that black beard, said Poirot thoughtfully, as we walked out into the hall again. 
Poirot thought very much about the black beard as he walked around the old house.
mnli hypothesis: Poirot thought very much about the black beard as he walked around the old house. premise: So Dorcas knows nothing about that black beard, said Poirot thoughtfully, as we walked out into the hall again. 