Wry neck, or torticollis, is a painfully twisted and tilted neck. The top of the head generally tilts to one side while the chin tilts to the other side. This condition can be congenital (present at birth) or acquired. It can also be the result of damage to the neck muscles or blood supply. Wry neck sometimes goes away without treatment.
In the quaternions, 0 is the additive identity. In the ring of functions from R to R, the function mapping every number to 0 is the additive identity. In the additive group of vectors in Rn, the origin or zero vector is the additive identity.
In arithmetic, the additive identity is. . This means that you can add 0 to any number... and it keeps its identity! The number stays the same! Let's look at the number 5. Anyway we try to add 0 to it, the 5 just keeps coming back as the answer. Go ahead and try it with any number you can thing of...