Also, cog in the machine. One who holds a minor but necessary post in a large organization, as in Frank knew he was just a cog in the wheel of this giant corporation. This term alludes to the role of the mechanical cog, one of the teeth on a wheel or gear that, by engaging other teeth, transmits or receives motion. Used figuratively since about 1930, it sometimes is put as small cog in a large wheel, emphasizing a person's lack of importance.

Also, slip a gear or one's gears . Lose one's ability to reason soundly or make correct judgments, as in She must have slipped a cog or she would never have gone out barefoot in December, or What's the matter with him? Has he slipped his gears? These slangy usages allude to a mechanical failure owing to the cog of a gear or a gear failing to mesh. The first dates from about 1930, the variant from the 1960s.