It’s happened a couple of times now, I’ve been sculpting away and then in trying to remove an unwanted area I end up with a polygon spike. However, no amount of smoothing or flattening would get rid of it. Can I ask, what’s the best way to deal with this sort of thing?
… and just for the record, I’ve not been using the snake hook brush! 
The poly count is obviously denser in that area than the rest of your model. You could try the SmoothPeaks brush then ClayPolish (Lightbox -> Brush -> Clay). There are lots of ways to get rid of it.
If you’re not concerned about clean topology however, I recommend looking into Dynamesh:
http://docs.pixologic.com/user-guide/3d-modeling/modeling-basics/creating-meshes/dynamesh/
http://pixologic.com/zclassroom/homeroom/lesson/dynamesh/
Enable PolyFrame so you can see the wireframe of the mesh. You may just be able to use the move points brush.
Dynamesh got introduced in Z3.5 (i think); whereas I’m running the trial version of 3.1