Wikiwackiness
Some time ago, after exposure to cats for the first time in all my born days, I'd been wondering what the purpose of purring† is, if there's some evolutionary advantage in it. I finally remembered to look it up and found this: Purring also "was a popular English folk sport practiced from at least the 16th century and likely before" whereby two opponents fought by kicking each other in the shins.
The British, man.
† Likely a sign that the cat is contented and is no threat. (For whatever it's worth, kneading, a similarly cat-distinct behavior I was baffled by, may serve an overlapping purpose: to show contentment – but to also prepare a surface for comfort, a partly retained but not-exactly-still-needed action, a "remnant instinct".)