Child attached to Player Parent spins Uncontrollably when Script is Attached

I've spent weeks trying to animate the objects on my player parent. My current challenge is when I rotate my parent object with torque, the children objects that I've attached scripts to, spin out of control even though the script conditions have not been met. Ironically, when I hold the objects still or move them forwards or backwards, they behave perfectly. No Rigidbody, Collider or other components are attached to the child object except Transform, Mesh, Mesh Renderer and Shader. Here is the script:

 public class AttackBite : MonoBehaviour {
     public float mandibleStartAngle = 80;
     public float mandibleStopAngle = 120;
     public float mandibleRotationZ = 0;
     public float animationSpeed = 15;
 
     void FixedUpdate () {
         //Bite
         if (Input.GetMouseButton (1)) {
             //Close Mandibles
             transform.localRotation = Quaternion.Slerp (transform.rotation, Quaternion.Euler (0, mandibleStopAngle, mandibleRotationZ), Time.deltaTime * animationSpeed);
         }
             else {
             //Open Mandibles
             transform.localRotation = Quaternion.Slerp(transform.rotation, Quaternion.Euler(0, mandibleStartAngle, mandibleRotationZ), Time.deltaTime * animationSpeed);
         }
     }
 }

Any help you can provide would be greatly appreciated. Thanks