In 1934, restoration work on this early 16th-centruy portrait by Raphael revealed that sometime in the mid-17th century, an anonymous artist had painted over it in places, transforming it into a representation of Saint Catherine of Alexandria holding a spiked torture wheel and a palm frond. (According to traditional narrative, the converted Catherine, after refuting the arguments of fifty pagan philosophers chosen by Emperor Maxentius and converting hundreds to Christianity while imprisoned, was condemned to death on a spiked breaking wheel; it shattered at her touch and she was beheaded, becoming a martyr.)
When this layer of overpainting was removed, a little unicorn was revealed—a traditional medieval symbol of purity. Later, in 1959, further restoration work revealed that a dog was hidden under the unicorn; in this case, the overpainting had been done by Raphael himself.
However, you can still see—and now won’t be able to unsee—the two floppy puppy-dog ears on either side of the unicorn’s head.
Raphael: Portrait of Young Woman with Unicorn (circa 1505 – 1506).