Let's say you're a evil Serial Killer
who wants to make a 'bold statement'. So what do you do? You take one of your victims, chop off the sucker's head and mail it to the cops in a cute little gift box wrapped up in a pretty bow.
It doesn'y have to be a head, or even human, or even giftwrapped. You can send or leave any gruesome body part to freak out your enimies. Think the horse's head scene from the Godfather series