No idea why they do it gravy, but loads of them do, i presume you mean after you have clipped the dogs nails? or are you cutting yours and feeding them to the dog? either way lots of dogs will eat them, never tried to eat them myself. give it a go and let us know how you get on, you can eat the dogs and the dog can eat yours.
Full of calcium ..... and if you live near any horses and spot the farriers showing them at some time, stop and ask for some hoof clippings..... your puppy will be your best friend forever then. My dogs have always been around my horses and the only time a fight has broken out is over the last bit of hoof trimming at shoeing time. It's the same principle with dogs gnawing on bones, although not all bones are safe for dogs as I am sure you are aware. Hope that helps.