The aversion of the Beaver's eyes is motivated by the primitive belief that whatever cannot be seen by oneself, cannot itself see you. This charming simplicity of thought is the innocent basis of most epistemologies, and it can be said, with some justice, that all of Western philosophy is but footnotes to the nursery-room game of peek-a-boo.
And so … we are indulging in a pre-Socratic, preschool tautology of existential hide-and-go-seek … the Beaver dematerializes her stony-faced surrealist nemesis the Butcher by averting her eyes. Lewis Carroll disarms his Boojum by composing the Snark backwards and thus placing the former into a perpetually receding, invisible future of the latter.
As for myself, I'm one of those literal-minded draughtsmen who cannot draw what he cannot see. I shall spurn Rule Number One of Illustration (if you cannot draw it, place a bush in front of it) for I am above such petty stratagems — a plague on all manner of foliage, those leaves, so many, so many, is there no end to them? The naked Boojum shall remain a naked, undrawn, unseeing Boojum.
To see a Boojum, ladies and gentlemen, is to be seen by a Boojum! Eschew the lethal gaze of all negating nonentities and all will be well! Focus instead your nondiscerning gaze upon the perfectly rendered nonchalance of this cool drawing. Nothing to see here folks, just move right along.