R. Austin Freeman, A Silent Witness — Chapter 13 (1915)
“ People who sit opposite in a public vehicle unconsciously regard one another, as I was doing myself; but when I had met my neighbor's eye a dozen times or more, I began to grow annoyed at his persistent inspection; and finally, shutting up my book, proceeded to retaliate in kind.This seemed to embarrass him considerably. Avoiding my steady gaze, his eyes flitted to and fro, passing restlessly from one part of the vehicle to another; and then it was that my medical eye noted a fact that gave an intrinsic interest to the inspection. The man had what is called a nystagmus ”
