text: I suppose , I may not ask you , monsieur , what first led you to suspect the fact ? " Poirot smiled and answered : " A scribbled over old envelope , and a freshly planted bed of begonias . " John , I think , would have pressed his questions further , but at that moment the loud purr of a motor was audible , and we all turned to the window as it swept past .
  
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  We all heard a vehicle go by outside .