The terrifying dog in the Hound of the Baskervilles is described as having 'blazing eyes' and a 'luminous muzzle', appearances attributed by Watson and Holmes to the application of phosphorus. Review of the toxicity and flammability of white phosphorus make this improbable. It is suggested that Conan Doyle's description was probably influenced by knowledge of the recent and much publicized discovery of luminescence due to the radioactivity of uranium salts.