Drew wondered if somehow being so well-trained in searching would make them immune to missing large hairy gorillas. “You might expect that because they’re experts, they would notice if something unusual was there,” he says.

And so he took a picture of a man in gorilla suit shaking his fist, and he superimposed that image on a series of slides that radiologists typically look at when they’re searching for cancer. He then asked a bunch of radiologists to review the slides of lungs for cancerous nodules. He wanted to see if they would notice a gorilla the size of a matchbook glaring angrily at them from inside the slide.

But they didn’t: 83 percent of the radiologists missed it, Drew says.