Jonathon Crystal, a psychologist at the University of Georgia, found out that rats are capable of a form of complex thinking previously attributed only to humans and primates: they can think about what they know or do not know:
Humans are often aware of what knowledge they possess or lack and what they are or are not capable of.
"Imagine, for instance, that you're a student going into a classroom to take an exam," Crystal said. "You will often have some idea how well you're going to do on the test. You know before you answer the questions whether you know or don't know the answers. This pretty complex form of cognition, known as metacognition, is at the heart of the human condition."
Here's the experiment:
Rats were given a choice to take a test. If they bailed out of the test by poking their noses into one hole, they received a small reward of food pellets. If they opted in by nudging their snouts into another hole, passing the test resulted in a large reward of pellets, while failure yielded nothing.
The test played the rats noises that were either short (between 2 and 3.6 seconds) or long (between 4.4 and 8 seconds). The rodents then had to classify the recent noise as either long or short by pressing one of two levers. This choice was relatively easy if the noise was either very short or very long—for instance, 2 seconds or 8 seconds. However, the decision was far harder if the noise was easily confused as either short or long—for instance, 4.4 seconds.
The scientists found the rats appeared capable of judging whether they had enough information to pass the test. The more difficult the test was, the more often rodents opted to decline the test.
http://www.livescience.com/animalworld/070309_rat_thinkers.html