Ultrasound is an inaudible sound that is capable of influencing the behavior of a person. It can also be used to perform various medical procedures, such as breaking the bones of a patient, or to help the patient to relax for a surgery.

This sound is also capable of causing a temporary loss of consciousness, and even of making a person believe that he is in an anesthesiological state.

The use of ultrasound in this manner is known as "sonography". It was discovered in the late 19th century, and since then, it has been used in many areas of medicine and biology.

For example, it is used to measure the length of a person's skull, to count the number of heartbeats per minute, to check the flow of blood through a blood vessel, and to measure the size of a tumor.