To err is human, to purr is feline.

And metaphors like cats behind your smile,Each one wound up to purr,each one a pride,Each one a fine gold beast you've hid inside (...)

Jim slept deeply, lulled by the rhythmic rumble of the purring Pye.

No one has ever been able to discover how they make this subtle sound, and what is more, no one ever will. It is a secret that has endured from the very beginning of the time of cats and will never be revealed.