I have always given my tortoises artificial cuttlebones from the petstore, which are marketed toward birds. I have always left the backing on, as I thought it was a more dense form of calcium, and have never had a problem. However, now some folks are saying it's made of plastic? Is that true? If so, that can't be good for tortoises if they swallow it. Does anyone know what it's actually made of? If it's not natural, then I will have to switch to real cuttlebones, because the sound of scraping calcium away from the backing would drive me bonkers.