The Roosters' Dilemma

I enjoyed reading this about John Napier, inventor of logarithms:

Napier used this rooster to find out which of his servants had been stealing from his home. He would shut the suspects one at a time in a room with the bird, telling them to stroke it. The rooster would then tell Napier which of them was guilty. Actually, what would happen is that he would secretly coat the rooster with soot. Servants who were innocent would have no qualms about stroking it but the guilty one would only pretend he had, and when Napier examined their hands, the one with the clean hands was guilty.^[5]