Cracking One's Sternum. Really?

Recently a friend told me that since she's been doing Bikram yoga regularly her sternum has popped a couple of times....and that it is crazy.  This revelation led me to realize that I apparently don't know what a sternum is.  To the extent that I thought I knew, I imagined it to be a solid piece of bone and not something capable of "cracking".  So.....what the hell?

 

It turns out I do know what a sternum is.  Or, at least, pretty much.  It is actually a big 'ol piece of bone in the middle of your chest. It isn't jointed in any way.  For some reason that makes me feel a lot better.  I don't want my heart parts cover to be jointed.  I want a solid wall of defense.  However I found out via Wikipedia that it is connected to your ribs by cartilage (which i guess connects with some kind of joint but a different kind....some non-standard joint) and is connected to your clavicles by joints.  So I think that what is popping are those joints, which sounds heinous.  There seem to be about equal opinions on the internets about whether it's totally awesome and okay or whether you should immediately take your cracky sternum to a chiropractor.  That's really neither here nor there, i just wanted to know if it was possbile.  And I guess it is....kind of.  There was a lot of stuff about it on yoga forums but also lots of stuff out there in the internet about it happening when people stretch in the morning and stuff like that.  So, basically it's a stretching thing.  The lesson here?  Never stretch anything, if you can help it.

Wikipedia tells you about your sternum and shows you diagrams.

Sternums cracking on a bike forum.  The tenth post down is kind of the only one that sounds remotely informed.

And here is a pretty awesome video of a guy doing some kind of thing with his body.  Seems like it might get some stuff to crack.  Also, he yells at you to giggle a couple of times and then giggles maniacly himself.  It's worth waiting for.