I am not mathematically smart. This is going to be fun 
I’ve got a humanoid rig on scene where I am using script to twist the spine, atm it “works” but it’s not pretty.
The gameplay is a “3rd person over the shoulder esque” shooter, and for the firing mechanism i want the hip to maintain rotation while blending rotation up the spine until the neck/shoulders are aiming where the player is shooting. At the moment for short hand I have the bottom spine simply LookAt(targetPos), it works, its ugly.
What I’m trying to do is get the rotation between two rotations, i have the base object facing the direction the player is moving and the top of the spine aiming where the player is shooting, i want to script the other spine bones to face between these angles… am i making any sense? 
so i want;
A - base rotation
B - middle rotation
C - end rotation
A is set by WASD, C is set by raycast.mousepos.
i want the half way point between A and C to apply to B.
as always, sorry for my terrible explinations and/or over-complicating a simple question maybe i never know lol
p.s.- I would love some kind of “Quaternion nextRot = quaternion.lerp (A, B, time, return nextStep)”