There were matters of science at issue, and there were matters of life, common decency, mercy. "As the wretched beetle was still feebly alive," he told Crick, "I have put it in a bottle with chopped laurel leaves, that it may die an easy and quicker death." Any naturalist of his day knew that laurel leaves, when chopped, release prussic acid, containing hydrogen cyanide. Darwin didn't want his last beetle to suffer. He was a gentle man, quite aware that he'd already caused discomfort enough.
--David Quammen, The Reluctant Mr. Darwin