He tied a knot with his tongue he couldn't undo with his teeth.

Understand the thought

Meaning in plain English

A spoken commitment can create an obligation that is difficult to undo. Consider what you are agreeing to before making a promise that later effort or regret may not easily release.

What the words are saying

The tongue ties the figurative knot through words, while the teeth cannot undo it by force. The contrast shows how an apparently easy statement can have consequences that are harder to reverse. A promise, agreement or public declaration may shape what other people rely on. The proverb does not determine the legal effect of any particular words, and commitments can sometimes be changed by a clear mutual agreement. Its useful warning is to think before accepting an obligation, and to communicate promptly if circumstances make it unworkable rather than assume that wishing it away is enough.

Everyday example

A volunteer checks the dates before promising to run every session, recognising that others will arrange the programme around that commitment.

When to use it

Use it before a promise that others may reasonably rely upon.

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Agent-assisted editorial interpretation. This explains the words; it does not by itself verify their author or earliest origin.