His aversion to heretics and infidels was so great that he seemed to know them by their smell. Thus, when he was once traveling from Milan with a large company on horseback, he conversed freely with all but one, who he said smelt like a heretic; and so indeed the man turned out to be. He remembered the counsel of St. John, not even to salute or eat with infidels, and so would have nothing to do with them or with Jews, especially with those who showed no respect at all for our religion.
The Life of St. Camillus of Lellis by Father Sanzio Ciccatelli, trans. by Father Frederick Faber. p. 207