Neck cycle during gaits?

Hello, I'm just now getting into gait programming and playing with sensors on my Bittle (with the ESP32 board).

Quick question after digging through the source for OpenCat... gaits seem to only define the shoulders and elbows unless I'm mistaken.

Where is the head/neck turn cycle coming from? With additional weight in the front, head motion appears to be throwing the balance off quite a lot and I'd like to be able to control that.

Thanks!