Francis Hobart Herrick,
Audubon the Naturalist: A History of His Life and Time…
“ The black snake does all the things which are here so minutely described—pursuing its prey with astounding agility, constricting about it as a prelude to swallowing it, ascending trees readily, coiling when brought to bay as if about to strike, and even vibrating the tip of its tail on the ground or leaves, as if in emulation of the genuine rattler, a kind of behavior which was looked upon by Darwin as a case of protective mimicry. No one could have known the rattlesnake better than Audubon from his constant encounters with it in the field ”
