The head is one of the hardest targets of the body to hit. It's small (compared to the rest of us), moves on a flexible base (the neck) and is a little high off the ground. Practicing high kicks and strikes increases accuracy, body positioning, footwork, flexibility and speed. Constant practice also generates more power in the way the muscles of the body move. The Headhunter workout is for you to try and aim your kicks and strikes as high as you can. Start with your own head height (or as close to it as possible) and try and improve, progressively, on that. You can stick to just one dominant side if you want, but for better balance in the way you train your body it will be better if you change lead legs with every set, completed.
Extra Credit: 30 seconds rest between sets.