The "Extra-terrestrial Hypothesis" or "ETH" is the idea that some UFOs may be spacecraft sent to Earth from another civilization or space other than earth, or on a planet associated with a more distant star. Among the most common reports of supposed alien encounters involve the Greys. Grey Aliens are typically depicted as dark grey-skinned diminutive humanoid beings that possess unusually large heads in proportion to their bodies. They are depicted as having no hair anywhere on the body, including the face, and no noticeable outer ears and very small noses and mouths. They are also depicted as having very large opaque black eyes with no discernible iris or pupil.