While touching the core is not harmful, it continually grows in size, restricting the available space for movement. Two sets of control rods protrude from the kill wall; if the player knocks particles into all the rods of one set, the core shrinks to its minimum size before starting to grow again. The player starts the game with a limited number of decoys, which can be deployed by pressing the Decoy button in order to lure particles toward the kill wall, control rods, or either of two small "bonus chambers" at opposite corners of the screen. An extra decoy is earned by knocking out both sets of rods.