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Feynman wrote about this decades ago

He may of told the story in other places, but I remember that it was discussed in the book Surely You're Joking, Mr. Feynman!.

He would act as a bloodhound, smelling books, then having people handle the book without him present, then identifying which book a person handled by smelling their hands. I believe he did it also with playing cards after identifying the differences in the way people's hands smelled.

Try it, it works really well! But it was the difference between untouched and a handled book. It’s really obvious when you smell closely.

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