slip a cog

Idioms  

1. Also,. 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.

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Example Sentences

On the second round, he seemed to slip a cog on the par-three fifth hole.

From Time Magazine Archive

I will try to answer your questions, but you know after a lapse of forty years, one’s memory may slip a cog.

From History of 'Billy the Kid' by Siringo, Chas. A.

Perhaps this causes his romanticism to slip a cog, to run at times on a side-track, to become the servant of his religious partisanship.

From Lincoln; An Account of his Personal Life, Especially of its Springs of Action as Revealed and Deepened by the Ordeal of War by Stephenson, Nathaniel W. (Nathaniel Wright)

They will go on prospering; there is no further reason why he should bend a wire, slip a cog, or delay the hurrying wheels.

From Floyd Grandon's Honor by Douglas, Amanda Minnie

"Yes, if they have had any warning or if our plans slip a cog anywhere we shall be repulsed to a certainty."

From Bucky O'Connor by Raine, William MacLeod