The aim of the game is to propel oneself, a single-celled organism ("Mote"), into other smaller motes to absorb them. Colliding with a mote larger than the player will cause the player to be absorbed, resulting in a game over. Motes smaller than the player are blue, while motes bigger than the player are red. Changing course is done by expelling mass. Due to conservation of momentum, this results in the player's mote moving away from the expelled mass, but also in one's own mote shrinking. There are three different "zones" of levels in Osmos: In the "sentient" levels, the goal is to prevail over active motes of various types that hunt and absorb other motes, including the player. Hunting them typically involves absorbing as many inactive motes as possible before chasing down the active ones with the extra mass one has gained.