In chapter 7, Poirot mentions that he once found a clue, but since it was four feet long instead of four centimetres, nobody would believe in it. This is probably a reference to a situation which occurred in "The Murder on the Links", where Poirot found a piece of lead-piping which he concluded was used to disfigure the victim's face so that it would be unrecognisable. Nevertheless, the artefact was described in that novel as a piece of lead-piping only two feet long.