Cats and nail filing dust: what's the attraction?

Factual Questions
1

I know “cats is weird” is a sound general principle. But other than that, is there any factual reason why both our current cats, but no other cat I’ve ever lived with, might be totally jonesed to lick my used nail files? Doesn’t seem to matter what kind of file, whether sandpapery emery boards, traditional steel, or these newfangled glass ones. They come running from anywhere in the house if they hear me start to file, and I have to store the files inside something latched as they will claw up simple drawers to get at them. If they do manage to capture one, they’ll lick it well beyond clean and drag it off somewhere.

They are also the first fully indoor cats I’ve lived with, so I am wondering if the lack of crunchy little bugs, rodents, and small reptiles in their diet has anything to do with this behavior.

Any ideas?

2

Maybe they are intrigued to find something that feels so much like their tongues :).

A Google search shows that you’re not the only one wondering but yields no useful information other than some sketchy suggestion of fish glue used to adhere the emery to the board.

My old vet used to feed the clippings from our dogs’ claws to his office golden retriever, and now when we clip claws the rest of the dogs hover around to get yummy nail clippings. Maybe it fills some sort of a nutritional niche for them (keratin?), or maybe they just like the taste, being carnivores and all. Could be the cats are satisfying the same craving with your nail files.