Objectivity and again objectivity, and expression: no hindside-before-ness, no straddled adjectives (as "addled mosses dank"), no Tennysonianness of speech; nothing-nothing that you couldn't, in some circumstance, in the stress of some emotion, actually say.
Speech is often barren; but silence also does not necessarily brood over a full nest. Your still fowl, blinking at you without remark, may all the while be sitting on one addled egg; and when it takes to cackling will have nothing to announce but that addled delusion.