"The Surprising History of American Sniper's "Wolves, Sheep, and Sheepdogs" Speech" by Michael Cummings and Eric Cummings, www.slate.com. January 21, 2015.
Ralph Waldo Emerson (2010). “Essays and English Traits by Ralph Waldo Emerson: The Five Foot Shelf of Classics, Vol. V (in 51 Volumes)”, p.310, Cosimo, Inc.