How to rotate torso (sub mesh) of a model?

I've been trying to get the upper body / torso of a model (the player one from the AngryBots demo) to rotate to wherever the mouse pointer currently is.

The very simple C# code looks like this:

 public Transform UpperBody;
 
 void Start () {
 
 }
 
 void LateUpdate () {
     var ray = Camera.main.ScreenPointToRay(Input.mousePosition);
     RaycastHit hit;
     
     if(Physics.Raycast(ray, out hit, Mathf.Infinity)) {
         var hitPoint = hit.point;
         var rotation = Quaternion.LookRotation(hitPoint - UpperBody.position);
         UpperBody.rotation = rotation;
     }
 }

The public UpperBody field is set to the root bone (the spine in thise case) of the upper body. And while the model does rotate as I move my mouse, it is not correct as he keeps looking straight up in the air and is rotated away from my mouse:

I've been thinking it probably has something to do with the fact that the origin of the local coordinate system for the spine doesn't have standard up/left/forward angles, like this:

But even if this is the problem, I have no idea of what I need to do make it rotate correctly.