I've gotten one of these cradle cap sponges with each of my children, and they have all come with that blue plastic piece. Does anyone have any idea what purpose it's meant to serve?
If you google "surgical brush with nail cleaner" you will have your answer. These brushes were designed for surgeons to clean their hands prior to surgery. They have been re-purposed for removing cradle cap, and the nail cleaner is just part of the package. They are designed for single use.