In the Doom engine, the wall wiggle bug, also known as the floor wiggle or wobbly line bug[1], is a graphical glitch most often apparent when a player is positioned in such a way that a two-sided linedef passes almost directly through the center of the player. Due to the nature of the glitch, it is generally observed when the player is standing at the boundary between two sectors with different heights, such that there is a ledge visible above or beneath the player. The glitch results in the line demarcating the ledge appearing to "wiggle" back and forth in a distracting and unrealistic manner as the player moves.