In addition to nonhuman primates, other animals are also shown metacognition. Foote and Crystal (2007) provided the first evidence that rats have the knowledge of what they know in a perceptual discrimination task. Rats were required to classify brief noises as short or long. Some noises with intermediate durations were difficult to discriminate as short or long. Rats were provided with an option to decline to take the test on some trials but were forced to make responses on other trials. If they chose to take the test and respond correctly, they would receive a high reward but no reward if their classification of noises was incorrect. But if the rats decline to take the test, they would be guaranteed a smaller reward. The results showed that rats were more likely to decline to take the test when the difficulty of noise discrimination increased, suggesting rats knew they do not have the correct answers and declined to take the test to receive the reward. Another finding is that the performance was better when they had chosen to take the test compared with if the rats were forced to make responses, proving that some uncertain trials were declined to improve the accuracy.