My initial reaction to this was, &quot;Wait, didn&#x27;t we know this already?&quot; The key to the story is somewhat buried:<p>&gt; The bubbles then stick around for about 20 to 30 minutes, and you won’t be able to crack your knuckles again until they are gone — a sure sign that <i>the sound is not caused by bursting bubbles, as was the leading hypothesis for many years</i>.