Scientists have long known that humans, higher primates, dolphins and some birds demonstrate “metacognition” — the ability to think about thinking. We know when we know something, and we also know when we don’t know something.

But now a study has shown that even rats can demonstrate metacognition. Jonathon Crystal, a neuroscientist at the University of Georgia at Athens, working with his student Alison Foote, figured out a clever experiment to test rats’ awareness of their thinking. They presented the rats with a “sound classification” test: They trained the rats to associate a long, 8-second burst of static with pushing one particular lever, and then trained them to associate a short, 2-second burst of static with a different lever. They’d play one of the two sounds, and if the rats pushed the correct lever, they’d get six food pellets; pushing the wrong lever got them nothing. The rats quickly learned to distinguish the two sounds by duration, and ate tons of pellets.

The scientists also offered the rats another opportunity for food: When they heard a burst of static, they could simply stick their noses in a food trough and get half the reward — three pellets. But the rats preferred to push the levers, because they were good at distinguishing the two sounds, and it gave them a much bigger reward.

Then things got interesting. The scientists made the test harder. They started playing bursts of static that were of intermediate length — four seconds, five seconds, six seconds — and thus harder to classify as “long” or “short”. Suddenly, the rats decided to forgo the test and simply stick their noses in the food trough to get the smaller reward. Apparently, the rats realized that they were now unlikely to pass this much-harder test, so they skipped it. As the scientists put it in a press release:

“Our research showed that the rats know when they don’t know the answer to a question,” said Crystal.

I confess I find it mindblowing how often we discover the complexity of the mental lives of seemingly dumb animals. Octopuses in captivity play complex games to alleviate boredom; grey parrots grasp the concept of zero; and now rats demonstrate a level of self-awareness about their cognitive limitations that many humans don’t possess.