Ellen Emerson writes to her brother Edward:
Father [Ralph Waldo Emerson] is constantly engaged now in writing and reading about Mr Thoreau and you had better keep a mem. of what you will ask for when you get home, and put down on it Mr Channing’s [William Ellery Channing] quotations from Mr Thoreau’s journal. They are very nice and Father likes to read them. One of them Father considers a question for a gameparty. “Some circumstantial evidence is very strong, as when you find a trout in the milk.” Father wanted I should ask the gameparty what that proved. I saw the moment I heard it and considered it so self evident as to be not worth mentioning, and long afterward Mother [Lidian Jackson Emerson] said “Or a mouse.” Then I explained to her that wasn’t the same thing, that it meant the milk was watered. Whereupon Father said he hadn’t thought of that before, of course that was right. I was amazed that he shouldn’t have seen it, but on trying the experiment I find that very few people do.
(The Letters of Ellen Tucker Emerson, 1:274)