Crackles are caused by the "popping open" of small airways and alveoli collapsed by fluid, exudate, or lack of aeration during expiration.
René Laennec adopted the existing word râles (which has been translated as "rattles", "groans" and otherwise) to describe the added breath sounds that are now referred to as "crackles".
He described them using unusual daily examples, such as "whistling of little birds", "crackling of salt on a heated dish", "cooing of the woodpidgeon", etc., but he soon realized that he was unable to use the term in front of his patients because it conjured the association of le râle de la mort, which translates to "the death rattle", the noise that people who are about to die make when they can no longer clear secretions.
[6][7] The term rales is still common in English-language medical literature, but cognizance of the ATS/CHEST guidelines calls for crackles.
In 2016, the European Respiratory Society reported on a study of various physicians listening to audiovisual recordings of auscultation findings and interobserver variation was analyzed.