A stoat’s pelt transforms from brown to white in winter, during which time it is more commonly known as an ermine. Accepted wisdom in the West held that if the animal’s spotless coat was dirtied, it would immediately perish—making it a prime symbol of purity (and occasionally justice). Appropriately, the ermine features prominently in this painting of Elizabeth I of England, the “Virgin Queen.” More oblique is the animal’s inclusion in Leonardo’s 15th-century portrait of the less-than-chaste Cecilia Gallerani, mistress to the Duke of Milan. The painter may have been nodding to the duke’s recently awarded insignia for the Order of the Ermine, or making a sly reference to his lover’s last name (Gallerani bears a resemblance to galay, the Greek word for ermine).