Press F2 and enter any of the following codes, then press F2 again to confirm. 

dh3beacon       Irresistible to animals
dh3damper       Objects make no noise
dh3f13          Excess gore   
dh3find         Brings you to the nearest deer
dh3homegym      No fatigue
dh3ice          Snow  
dh3leadeye      Bullet cam 
dh3monster      Big deer 
dh3nofear       Animals are not afraid of you
dh3plague       No animals
dh3sightin      Sights in your gun
dh3skyhook      Enables you to fly
dh3thor         Thunder
dh3water        Rain  
dh3zeus         Lightning  
dh3tracers      Shows the path of the projectiles
dh3showme       Shows deer on the map