When a cat purrs it starts in its brain, sending messages through its neural oscillator to its laryngeal muscles. This causes a twitch to happen at the rate of 25 to 150 vibrational Hz per second. The vocal cords then separate and when the cat inhales and exhales, the sound of a purr can be heard. Amazing!
Why they purr is not exact science, but many believe it to be a form similar to that of a human’s smile. A human will smile when they are happy, nervous, scared or when they want something. A cat will purr in happiness, fear, begging and yes, when they are nervous too. This allows them to not only communicate with us, but also other cats around them.