Many physiological adaptations fit the animal to its lifestyle. It burrows, and can tolerate high levels of carbon dioxide. Its ear is sensitive to low-frequency sound, which may be ideal for detecting sounds emitted by termites and ants underground. The leathery snout is covered in mechano- and thermoreceptors. These receptors provide information about the surrounding environment. The echidna has a well-developed olfactory system, which may be used to detect mates and prey, and its other senses perform well. Its brain and central nervous system have been extensively studied for comparison with placental mammals.