[247] therefore the sheep, as being the most excellent of animals, is a symbol of the purification of the most excellent part of man, the mind. And birds are an emblem of the purification of the speech: for speech is a light thing, and winged by nature, flying and penetrating in every direction more swiftly than an arrow. For what is once said can never be re-called; [173] but being borne abroad, and running on with great swiftness, it strikes the ears and penetrates every sense of hearing, resounding loudly: but speech is of two kinds, one true and the other false;