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On today’s edition of “Strange mathematicians”:
John Napier, inventor of logarithms back in 1614, dabbled in necromancy and alchemy in his life time and was believed to be a real magician.
He used to carry a black cockerel with his as his “familiar” and used it to detect which of his servants were stealing from him.
He used to lock the suspects in a room with the cockerel and tell them to stroke it, adding that the magical bird can detect any guilty individuals when stroked.
In reality, the cockerel was covered in a thin layer of soot, and since people believed him, the innocent would have no issue with stroking the cockerel.
The guilty however, would not fall for the trap of going anywhere near the mystical cockerel. Unwittingly admitting their own guilt with their clean hands. 
