"Sir William Gull has just brought me the enclosed quotations from Chaucer, as illustrations of the closure of the eyes in effort. [In "The Nun’s priest’s tale" in Canterbury tales the fox tricks Chanticleer into crowing, whereupon Chanticleer closes his eyes to make the effort (and gets seized by the fox).] He begs me to send them to you.
I have lately seen a terrier who very distinctly frowns during mental excitement – not always with anger, but often, I think, with anxiety, as in expecting food."