Ninjas Hate Surprises

I drew this a long time ago in class because I needed something to distract me from learning. And when I got back to the apartment, I just had to color it, because it was too funny to leave alone. Not exactly the finest work of art out there, but then again, that's not the reason I posted it.
Also - I'm not sure, but does this qualify as 'mature content?' I mean, that one guy's head fell off, but I still think it's cuter than it is violent.