Q. Is one allowed to swallow the nails that he cuts with his teeth?
A. Poskim disagree. Doleh Umashkeh (p. 145) quotes Ben Ish Chai that one should not tear his nails with his teeth, as he may actually swallow a piece and transgress on a Biblical prohibition. However he is lenient, but on the onset one should avoid doing it.
Kaf Hachaim (Y. D. 79: 11) adds concerns that one may eat also some of the skin itself (See next question) or that out of being accustomed, he may do it also on Shabbos.
Torah Lishmah (213) deals with nails that fell into a boiling cooking pot, if the food may also be prohibited due to the ‘Ba’al Teshaktzu’ prohibition or eating something disgusting. He mentions also that on the onset one should not eat the cooked food, since there is a ‘Ruach Ra’ah’ or spirit of impurity resting on cut nails.
Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit’a.