Warhorses fans will know why I am quoting this bit of Diamonds Are Forever:
"The word in Pinkerton's is that the Jockey Club are going to change to photos of the night eyes."
'"What are night eyes?"
"They're those calluses on the insides of a horse's knees. The English call them 'chestnuts'. Seems they're different on every horse. Like a man's fingerpirints."