Half-Life is a first-person shooter (FPS) that requires the player to perform combat tasks and puzzle solving to advance through the game. Unlike most of its peers at the time, Half-Life uses scripted sequences, such as a Vortigaunt ramming down a door, to advance major plot points. Compared to most first-person shooters of the time, which relied on cut-scene intermissions to detail their plotlines, Half-Life's story is told mostly using scripted sequences (bar one short cutscene), keeping the player in control of the first-person viewpoint. In line with this, the player rarely loses the ability to control the player character, Gordon Freeman, who never speaks and is never actually seen in the game; the player sees "through his eyes" for the entire length of the game. Half-Life has no levels; it instead divides the game into chapters, whose titles briefly appear on screen as the player progresses through the game. Progress through the world is continuous, (except for short loading pauses) with each map of the game connecting directly to the next, with the exception of levels involving teleportation. The game regularly integrates puzzles, such as navigating a maze of conveyor belts or using nearby boxes to build a small staircase to the next area the player must travel to. Some puzzles involve using the environment to kill an enemy, like turning a valve to spray hot steam at their enemies. There are few bosses in the conventional sense, where the player defeats a superior opponent by direct confrontation. Instead, such organisms occasionally define chapters, and the player is generally expected to use the terrain, rather than firepower, to kill the boss. Late in the game, the player receives a "long jump module" for the HEV suit, which allows the player to increase the horizontal distance and speed of jumps by crouching before jumping. The player must rely on this ability to navigate various platformer-style jumping puzzles in Xen toward the end of the game. For the most part, the player battles through the game alone, but is occasionally assisted by non-player characters; specifically security guards and scientists who help the player; the guards will fight alongside the player, and both guards and scientists can assist in reaching new areas and impart relevant plot information. An array of alien enemies populate the game, including headcrabs, bullsquids, vortigaunts, and headcrab zombies. The player also faces human opponents in the Hazardous Environment Combat Unit (a fictional special forces unit of the United States Marine Corps), and Black Ops assassins. Half-Life includes online multiplayer support for both individual and team-based deathmatch modes. It was one of the first mainstream games to use the WASD keys as the default control scheme.