Dog grabs and eats dog fur

[R. Bear]

My friend has a German Shepherd and I help brush all the shedding undercoat at this time of year. Problem is my 9 year old Min Pin will grab the clumps of hair that come off the comb and eat mouthfuls of the stuff. I have searched around and it does appear that this isn't as rare as I thought, but does anyone know WHY a dog (or any other living being) would find a mouthful of hair to be palatable? And will this behaviour cause any damage to the dog? He seems to be ok but he's so obsessed that I think from now on I'll tie him up out of reach while I help brush the Shepherd since I just don't feel that this can be a good thing..