Bearclaw Valley Why is the raven like a writing desk?

the girl stumbled into a tree and there her speed changed;
merrick, lunging after, arielle sweeping in; they converged upon the hapless child.
the bruin-heart struck first.
the bruin-witch aimed his shoulder at the fleeing stranger's ribs, hoping to knock the breath from her and send the half-grown wolf spinning into another trunk.
he laughed; pinball, he and arielle the razor-edges into which the trespasser bounced again and again.