Houndeye

The Houndeye is one of the alien species which appears in Black Mesa following the opening of a portal to Xen, and has an appropriately alien appearance. Possessing three legs and only a thorax, the Houndeye is a faint yellow-green in colour, with electric blue tiger-like stripes adorning the spine of the animal. In place of a head there is a large, black, compound eye that is protected by a single eyelid. They apparently communicate through a series of high-pitched sounds somewhat similar to the barking of dogs.

The Houndeye is an excellent example of a social animal in terms of pack hunting. While a shy and timid creature by itself, groups of three or more creatures display resonant behaviour, emitting destructive harmonics capable of injuring those they attack. This behaviour came about through Valve's original plan of Houndeyes being neutral or even friendly towards the player, until they realised that playtesters mowed them down regardless and dropped the idea.

Although they are not seen displaying this trait often, Houndeyes appear to be carnivorous creatures, as one is seen eating a dead security guard in Half-Life: Blue Shift. A Houndeye's mouth is located on the underside of its belly, close to the eye, filled with what appears to be fang-like incisors.

The Houndeye is the only remnant of a type of creature that was to be more common in Half-Life. Originally there was to be a "Panthereye" creature, similar to but stronger than the Houndeye. The Panthereye was re-integrated into a Half-Life mod called Point of View, which allows players to take the role of a Vortigaunt.

According to the book Half-Life 2: Raising the Bar Houndeyes were one of the enemy types in the early Half-Life 2, first seen by the player on an old projector slide in which they and bullsquids terrorized an American suburb. The texture for the Houndeye's compound eye was to shine and could reflect its surroundings. Houndeyes could also work in herds, led by a dominant Houndeye, and had faster movement speeds.