The worst that may happen if an insect crawls into your nose or ear is an infection (rarely, it can spread from the sinuses to the brain). In the tropics, where there are more insects, particularly in situations of severe bug infestations in the house, reports are most prevalent. But even in less-infested countries, people still report hearing insects with their ears. The human ear consists of three main parts: the outer ear, the middle ear, and the inner ear. The outer ear collects sound waves and directs them toward the middle ear. From here, the sound waves continue into the fluid-filled cochlea within the inner ear. The cochlea is divided into two parts: the small rounded cavity walled off by membranes called tectorials surfaces on which are mounted tiny hairs called cilia. The vibration of these hairs causes movement of water molecules inside the cochlea, which are sensed by special cells called neurons. These cells send signals through the auditory nerve back to the brain, where they are interpreted as sound. Insects have very sensitive hearing and will use sound to find food, shelter, and mates. They can also detect vibrations made by other insects who are eating them. This ability to hear each other's presence is called "cranialism" by scientists who study animals for this purpose. By using sounds waves, insects can locate each other from great distances.