I am currently taking an online ZBrush class through Gnomon; these are a few of my assignments. The human head was created using the "écorché" method. I sculpted a skull out of a sphere, sculpted muscles on top of the skull, then sculpted flesh over muscles.
The creature head was sculpted from a simple plane.
The topic this time was "Twisted Childhood Memories." Though I was too old for the cuddly glowing worms when they came out, I remember the countless ads for these things.