Marc Bekoff (2010). “The Emotional Lives of Animals: A Leading Scientist Explores Animal Joy, Sorrow, and Empathy — and Why They Matter”, p.19, New World Library
Aldo Leopold (2013). “Aldo Leopold: A Sand County Almanac & Other Writings on Conservation and Ecology: (Library of America #238)”, p.557, Library of America
John Milton (1760). “Paradise Regain'd ... To which is added Samson Agonistes and Poems upon Several Occasions, with a Tractate of Education. [With engraved plates.]”, p.206