OED defines them as:
nonchalant adjective (of a person or manner) feeling or appearing casually calm and relaxed; not displaying anxiety, interest, or enthusiasm
insouciant adjective showing a casual lack of concern; indifferent
blithe adjective showing a casual and cheerful indifference considered to be callous or improper: a blithe disregard for the rules of the road; happy or joyous: a blithe seaside comedy
So, what would be the difference between say, "a nonchalant shrug" and "an insouciant shrug"?
Also, what context are these words used in the following sentence:
"I would live all my life in nonchalance and insouciance Were it not for making a living, which is rather a nouciance." Ogden Nash, poet (Hard Lines, 1931)
Also, what does 'nouciance' mean? Is it simply a play on words?
Last, but most important, what word would best fit the following situation:
He was (nonchalant/insouciant/blithe) about the poor living conditions of the animals in his farm.