Charles Ellicott Commentary Ecclesiastes 7:6

"For as the crackling of thorns under a pot, so is the laughter of the fool: this also is vanity." — Ecclesiastes 7:6 (ASV)

There is again a play on words, which German translators represent by “the crackling of nettle under the kettle,” and Plumptre “the crackling of stubble which makes the pot bubble.” The reference plainly is to the quick blazing up and quick going out of the flame.