Purring

A noise that a domestic cat or possibly other creatures make to indicate well-being. A cat will also sometimes purr when it is uneasy or nervous, to seek reassurance.

How does a cat make the sound? - I don't know, would be good to put this in here

Science still does not know how cats purr, but one theory holds it involves cats false vocal cords, the other involving blood hitting the aorta

This article is a stub - you can help Wikipedia by fixing it.