Rats have a complex form of thought once known only in humans and other primates—specifically, metacognition, or the ability to mull over what one knows. Scientists at the University of Georgia gave rats a choice to either take a test or not. Passing the test resulted in a large food reward, failure yielded nothing, and opting out altogether led to a small reward. The test played noises of various durations that the rats had previously learned to classify as short (lasting two to 3.6 seconds) or long (4.4 to eight seconds). The more difficult it was to gauge the sound length—for instance, if the noise lasted 4.4 seconds—the more often rodents bailed out from the test. The findings, in the March 20 Current Biology, suggest the rats could judge whether they would pass or fail, hinting that metacognition may be more widespread than thought before.