There were no marks on Wilson's body except a small burn mark on his left hand, in which he was clutching a white bishop when he died, part of Savaronoff's set. As Poirot and Hastings enter the Doctor's flat, Poirot notices that the antique Persian rug has had a nail driven through it. After the proceedings in the flat, Poirot and Hastings return home and Poirot takes out a second white bishop. He weighed the one he took with the one Wilson was holding and discovered that the one he was holding was heavier. He explains that the bishop has a metal rod inside it, so that the current passing through the recently refurbished flat below is powered through the nail, into the also tampered-with table and into the bishop. The bishop was chosen because of Wilson's predictable first few moves (Wilson was electrocuted after playing the Ruy Lopez as White, consisting of the moves 1.e4 e5 2.Nf3 Nc6 3.Bb5 (see algebraic chess notation) – the square b5 was electrified and the white bishop with the metal rod was the light-squared one).