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

The saying figuratively rebukes someone whose own words have created a problem. A promise, claim, or rash remark may bind the speaker so tightly that later explanations cannot release him.

It emphasizes the lasting force of speech: what is easily said may be difficult or impossible to take back. The image contrasts making a verbal knot with being unable to untie it by practical effort.

Use it when a person is trapped by an earlier statement, especially after speaking too quickly, making an imprudent promise, or committing himself through words. It can warn someone before speaking or comment afterward on the consequences.