What are infrasound and ultrasound?

Ultrasound is above 18 kilohertz. Infrasound is below 20 hertz.

1.6cm &.1 A'

Bats use it to navigate their caves and dolphins use it to communicate. Mice also use it to attract mates. (Ultrasound)

Both are outside of our hearing range. They behave like the sound we hear.

Sound of a frequency below human hearing.