This ancient optical illusion is a 14,000-year-old puzzle

It works just like the classic rabbit-duck figure.

Mammoth Bison carved illusion
Your brain might detect familiar details like tusks and fur on the hunting tool, which was unearthed in 1973 at Southern France’s La Montagne Noire.Duncan Caldwell

This carved ornament was fixed on a hunting tool more than 14,000 years ago, but the illusion remains. Concentrate on the higher eye-​­shaped notch on the left side, and a tusk curves below it, revealing a mammoth. Stare at the one lower down, and that pointed tooth becomes a bison’s horn as the beast bows its head. You might recall a similar 19th-­century illustration: It’s a duck until the bird’s bill morphs into a pair of rabbit’s ears.

rabbit-duck illusion
The classic rabbit-duck illusion.from Fliegende Blätter, October 23, 1892

The rabbit-duck is a type of illusion called an ambiguous figure, and while we can’t know the ancient carver’s intent, this prehistoric knickknack is one too. According to Kyle Mathewson, a cognitive neuroscientist at the University of Alberta, the flip-​­flopping happens because the mammoth and bison share the same basic outlines. Your brain’s visual cortex makes sense of this low-level information, and then hands it off to a set of high-level processing neurons, which parses features like fur or tusks. This way, two different results stem from the same set of lines. ­Mammoth, bison; ­tomato, tomahto.

This story appears in the Spring 2020, Origins issue of Popular Science.