SilverWook said:
Since we're not seeing the front, there could be a center hub the head is attached to. I'm also making out seams in the "ball", so maybe this little droid can change it's body shape?
If the concept art is any indication, it looks after the head isn't resting on the main body as shown in the teaser. It's hard to tell in the concept art, but it looks like it may have a neck.