The Organ Grinder
Get at least one killshot on every organ.
This isn't too hard so long as you know where to aim. You'll easily get eye shots when going for headshots with the rifle. Aim for the top of the chest for the lungs and heart, middle of the midsection for the stomach, right of the midsection for the liver, just below the stomach for the intestine, and crotch for the testicle.