It entered the realm of psychology after the tale was discovered and adopted by Sigmund Freud. Schopenhauer's tale was quoted by Freud in a footnote to his 1921 work Group Psychology and the Analysis of the Ego (German: Massenpsychologie und Ich-Analyse). Freud stated that his trip to the United States in 1919 was because: "I am going to the USA to catch sight of a wild porcupine and to give some lectures."[1]