Artist and astrologer John Varley encouraged Blake to sketch portraits of the figures who populated his visions, called 'visionary heads'. The best known is the flea.Blake claimed that, while he was sketching the flea, it had explained to him that fleas were inhabited by the souls of bloodthirsty men, who were confined to the bodies of insects because, if they were the size of horses, they would drink so much blood that most of the country would be depopulated. The flea's bloodthirsty nature can be seen in its eager tongue, and the cup (for blood-drinking) that it is carrying.