Hi everyone! Dumb question number 693 - I've seen folks say to feed BOSS - which, I've finally figured out is Black Oil Sunflower Seeds - so actually this question has 3 parts: 1) (here's the stupid part) - shelled? or unshelled? 2) do you add it to their grain? free choice? just a treat? how much? 3) why??? what are the benefits? Thanks in advance!