Continuing with cracking myth's (no pun intended) I wanted to concentrate on something that I personally have an issue with, and that I have been chastised for over years because of this habit.
"cracking knuckles causes damage such as arthritis in the joints"
The cracking sound is actually the gases that are produced in the fluid that surrounds your bone ends i.e. joints being released from the synovial fluid once the joint capsule is stretched. This allows for better range of motion and stretches the tendons and muscles surrounding the joint capsule.
Yes, cracking knuckles can be gross. Sometimes I even cringe when I hear someone crack their entire back or do the hard twist of their head to the side thing. But no, cracking your knuckles is not the cause of arthritis. So next time your mother says to 'stop that' because it causes arthritis, you can tell her she's wrong. As a matter of fact it can actually decrease your chances of getting arthritis.
Instead you can tell her that it causes capsular joint loosening and eventually can lead to weakened grip. Sound better? Studies and testing are ongoing to prove this but cracking knuckles has been shown to lead to a correlation in decreased grip. So if you're a habitual cracker (I am under stress) then you may want to find another way to release the tension. Maybe a stress ball for while taking tests or count to ten and think namaste?