slip a cog

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.

Common Names:

Name	Pronounced	Usage
Neer	NAYR	Limburgish
Elias	ə-LEE-əsh (Portuguese), e-LEE-ahs (German), E-lee-ahs (Finnish), i-LIE-əs (English), ee-LIE-əs (English)	Portuguese, German, Swedish, Norwegian, Danish, Finnish, English, Greek, Biblical Latin, Biblical Gr
Nikias	-	Ancient Greek
Tore (1)	-	Swedish, Norwegian, Danish
Esmeralda	[.ezmə'rældə]
Yishai	-	Hebrew, Biblical Hebrew