The red-and-black splashes on the card are bustling with images: bad-tempered crows, a butterfly in a belly and even a couple of blood-stained kidneys -- if it isn’t a pair of monkeys contemplating ...

The simplicity of the stains' repeating patterns is key to why we see so many images in them. It’s easy to see familiar shapes in seemingly random patterns. Witness how many people see faces in clouds ...