E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Bit (of a horse).
To take the bit in (or between) his teeth. To be obstinately self-willed; to make up one’s mind not to yield. When a horse has a mind to run away, he catches the bit “between his teeth,” and the driver has no longer control over him.
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“Mr. X. will not yield. He has taken the bit between his teeth, and is resolved to carry out his original measure.”—Newspaper paragraph, April, 1886.
