A few more signal tricks rounded out the medicine advertising approach. Perhaps chief among these was the "secret ingredient." Every patent medicine needed something to set it apart from all the others making similar claims, some kind of mysterious element that was not and perhaps could not be fully explained. It fired the imagination, feeding hope where reason offered thin gruel. Carbolic smoke; swamp root; baobab fruit; and in the case of Clark Stanley's liniment, the secret was, of course, the magic of snake oil itself.

Tim Wu, The Attention Merchants, loc. 97