I think it might have been fine if you only added a rbody to the head for collision? But i'm geussing you tried that. Alternatively as long as you snake has colliders you could give the walls rbodies instead.
Also what your doing kinda sounds like re-inventing hinge joints, but doing it yourself does make it super flexible
Either way cool approach and thanks for letting me know, it seems to work well for the more fast paced nature of your game