Fact-Checking this Viral Bottle Trick

As an interesting side note, cavitation is also the reason for the noise of the "popping" sound you get when you crack your knuckles - or when your back or neck "cracks" when you move it certain ways, or even when you put some joints under a particular load, eg ankles cracking when you stand up sometimes after kneeling or crouching for a while. 

In these cases it's all about a specific, often sudden, pressure drop in the synovial (joint) fluid as the joint is partially tractioned (surfaces pulled apart). Unlike, as with propeller cavitation, the cracking/popping sound occurs as a gas bubble is formed - not as it collapses - and is the reason why a joint can't be re-"popped" for at least a few minutes. This is because the "pop" is the sudden release, or gasseation, of previously dissolved nitrogen from the fluid into a bubble rather than gasseation of the water molecules themselves. To "crack" the joint again it is necessary for the nitrogen to re-dissolve in the joint fluid and attempting too soon will not achieve the required sudden drop in pressure because the gas bubble will expand as you try.

BTW, this process is completely harmless and has no effect on the joint surfaces, in case you were worried! It categorically does NOT increase your odds of developing arthritis.