Diatomaceous earth will not affect the innards of an animal. This is due to the fact that DE particles are very tiny and their razor-sharp edges only function to lacerate surfaces at a microscopic level. Because insects are also small, the diatomaceous earth can easily cut their exoskeletons. The movement of their bodies across the DE, as well as their waxy exoskeletons, creates conditions in which the DE rubs against their bodies and lacerates their outer shell. A large, strong surface, on the other hand, such as the tissue of the intestines and stomach, is not affected by the sharp edges of the diatomaceous earth, as the particles are too tiny to cause any damage.
Image by David~O