IK - what am I doing wrong?

I am trying to rig a sheep. I can get the legs right based on tutorials but something about the head is wonky - as soon as I drag the target it starts spinning like the girl in the Exorcist. A little helpplease?

https://dl.dropboxusercontent.com/u/29556685/sheep.blend

sheep.blend (712 KB)

Your Head IK target is a child of the head. This means that it controls the head and the head controls it. This only works in government, and not very well even there.
Unparent the IK target from the head (in edit mode, Alt P) and all will be well.

BTW your leg pole targets are too close and the pole angles need to be changed for the left side to 180. Ideally, pole targets should be outside the arc of the chain they are controlling. That neck target is going to be a problem with the head spinning around as you bend it. You will have to limit the head bone’s Y rotation in the bone properties IK panel.

I only mention these because you might think it’s a parenting problem again but it’s not.