Motifs G0275.8.1. witch killed by placing salt or pepper inside skin while it is laid aside
Baughman has both English and U.S. references for this motif.
Piersen: "stress on the English origins of Negro witch beliefs would seem suspect in light of modern African anthropology. In both cases -- beliefs and tales -- it is probably that there was a cultural cross-fertilization or syncretism."
Baer says nothing about the witch rabbits, but I think this was important to Harris, and also to the book illustrators, as a way to weave the rabbit into the story, much like the way he uses the rabbit later on in Taily-Po and Impty-Umpty.