1. "Pareidolia is a psychological phenomenon involving a vague and random stimulus (often an image or sound) being perceived as significant. Common examples include seeing images of animals or faces in clouds, the man in the moon or the Moon rabbit, and hearing hidden messages on records played in reverse. The word comes from the Greek para- – "beside", "with", or "alongside"—meaning, in this context, something faulty or wrong (as in paraphasia, disordered speech) and eidōlon – "image"; the diminutive of eidos – "image", "form", "shape". Pareidolia is a type of apophenia."
2. An Introduction to Sine-Wave Speech