Pareidolia is the tendency to interpret a vague stimulus as something known to the observer, such as seeing shapes in clouds or seeing faces in inanimate objects or abstract patterns [1].

Pareidolia, as this experience is known, is by no means a recent phenomenon. Leonardo da Vinci described seeing characters in natural markings on stone walls, which he believed could help inspire his artworks. In the 1950s, the Bank of Canada had to withdraw a series of banknotes because a grinning devil leaped from the random curls of the Queen’s hair. The Viking I spacecraft, meanwhile, appeared to photograph a carved face in the rocky landscape of Mars [2].

This phenomenon also applies to the interpretation of radiological images. Metaphoric signs in radiology have been used for over 100 years. Metaphoric associations allow us to recognize and remember the imaging patterns of disease by the names we have given to them (e.g., the apple core sign in colon cancer, the onion skin periosteal reaction in aggressive periostitis, the bird's beak sign in achalasia, or the bear's paw sign in xanthogranulomatous pyelonephritis) [3-5].

But what happens when we see random look-alikes during our working day?

The result is an unexpectedly-amusing interpretation of normal and abnormal imaging findings, mainly for entertainment purposes.