They are a friskier, gaudier species than their fellows.
Cricket, as viewed from the fixed Stars.
"For this one purpose they appear to be kept and fed.

They do no other work, so far as I have been able to ascertain.

Carefully selected and trained, their mission is to go about the world looking for Balls.
Whenever they find a Ball they set to work to kill it.

But the vitality of these Balls is extraordinary.

There is a medium-sized, reddish species that, on an average, takes three days to kill.