Call of Duty Zombies began as a bonus mode in Call of Duty: World at War in 2008 and became one of the series' most recognized side modes. Sounds tied to Zombies spread widely through gameplay videos, compilations and short edits because they instantly suggest survival, panic and undead chaos. Even when a clip is short, fans recognize the mood right away. That is why Call of Duty Zombies audio still shows up in meme posts and gaming reactions years after the mode first became popular.