This animation was made using some bone constraints, a layer script, and by rotating just one bone. It uses the circular motion and converts it into a horizontal motion, that resembles a rotation around the y axis.
See for the layer script this thread, or download this zip archive with the layer script and an example file. Embed the layer script in a bone layer, create some bones, and then some orphaned bones (root and no childeren) with the same name, but ".tmp" attached to it. It attaches each .tmp bones to its master bone like glue, using bone translation, even if its master bone is rotated, scaled or translated. You can then use this .tmp bone to control other bones in your animation, using horizontal and/or vertical bone constraints of these bones to the .tmp bones.
This should make a head turn much easier. Wait what Heyvern has in store for us...
Edit: Here is the source file: constraints.zip
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