Subject: Crackin' Knuckles

Why do knuckles crack?  I've been told that it's because the movement
inside the joint creates bubbles that pop, but I don't believe that.
If that were true, the sound would be more like stepping on a bunch
of rice krispies.  And the popping movement of the offending joint
would be more of a sliding crunch.  Nope, I know there's something 
more.  Also, why do you have to wait to pop the knuckle again?  Not 
that bubble answer again!  How come my wrist, knees and vertebrae 
crack too?  All the same reason?  It feels different in my neck than 
my wrist.  
  Thanks, I've been searching for the truth for so long...

Re:Crackin' Knuckles