expression, suru verb (precursor)
stubbornly refuse to admit one is wrong
A classical idiomatic expression used to describe someone who obstinately refuses to acknowledge their mistake, often by making unreasonable excuses. The literal image is of rinsing one's mouth with a rock and using a flowing stream as a pillow, implying absurd contrariness.
彼は石に漱ぎ流れに枕すような言い訳をして、自分の非を認めようとしなかった。
He made excuses as absurd as rinsing his mouth with a rock and resting his head in a stream, refusing to admit he was wrong.
From the Chinese anecdote of 孫楚, who accidentally said he would “rinse his mouth with stones and use the stream as a pillow,” then stubbornly invented justifications for his words. The story made the phrase an emblem of refusing to admit an error.