Several of you asked us if cracking your knuckles causes arthritis, so we put our Verify team on it.

This led them to a study by the University of Alberta, which produced this video:

Scientists used an MRI machine to record knuckle cracks as they happened. In the video, you see a dark gray spot form between the joints; that's a cavity created in the synovial fluid, an egg white-like substance that reduces friction in your joints.

The creation of that cavity is what makes the cracking sound. And while it might look a little startling, researchers say it doesn't actually do any harm.

They're backed up by more research. A radiologist from the University of California, Davis found the same thing. Dr. Robert Boutin studied a group of people who crack their knuckles and a group who doesn't. He says there wasn't any difference in the health of their hands.

Researchers from Johns Hopkins University and MIT found the same thing.