In 1985, Perth, a researcher at Cornell University in New York, USA, observed a group of elephants and suddenly felt an intermittent vibration in the air. She also found that this vibration coincided with the tremor of an elephant's brow on his forehead. Perth concluded that this is a special way for elephants to communicate with each other.

Later, with her colleagues, Perth confirmed her conjecture with advanced ultrasonic recording instruments: the vibration she felt earlier was caused by low-frequency sound waves, which could not be heard by human beings and could be recorded on tape. The researchers also found that females communicate with males through concrete walls!

In rural areas, the elephant's cries heard by human ears will be absorbed by weeds and trees, and the propagation distance is limited; However, the low-frequency sound that people can't hear travels far away.

According to a hunter who rides an elephant, the elephant's hearing is very sensitive, and it can understand 27 different passwords. Scientists have also found that the elephant can distinguish extremely subtle music changes.

The reason why scattered elephants can act in unison is that the male elephant finds the female elephant in estrus for only two days a month, because the elephant has extremely sensitive hearing.