For Mark Twain there was a detail able to immediately make an interesting person: his relationship with cats.
The American writer, author of Tom Sawyer and Huckleberry Finn, had a deep passion for these animals and throughout his life he had many.
And, of course, their names also often bear the sign of his personality.
Cats associated with his life include names such as Baby and Buffalo Bill.
But it wasn't just a matter of domestic company.
Twain was deeply fond of felines and wrote several times about their intelligence and their particular character. In a short text of 1887, entitled An Incident, he came to formulate a very precise criterion: when he met a man capable of loving cats, he could consider it "friend and companion, without need for further presentations".
A phrase that tells something about the same Twain.
Born in 1835, Samuel Langhorne Clemens — his real name — built much of his fame by observing human beings with irony, seizing contradictions, weaknesses and strangeness.
Perhaps even for this reason he found so interesting animals that are hardly allowed to be commanded and that they give their confidence to their conditions.
More than a century away, its curious criterion of selection of people continues to seem surprisingly modern.
For Twain, discovering that someone loved cats did not mean to know everything about his character.
But it was definitely a great way to start.
And it is natural to connect that line to a still current idea: the way we treat animals can tell something about our character.