The purr is very important. It's the purr that does it every time. It's the purr that makes up for the Things Under the Bed, the occasional pungency, the 4 a.m. yowl. Other creatures went in for big teeth, long legs or over-active brains, while cats just settled for a noise that tells the world they're feeling happy.
Terry Pratchett, The Unadulterated Cat
cats, humor