Spring-Heeled Jack is a cryptid in English folklore. In Ken Gerhard's book, Encounters with Flying Humanoids, and his article on Cryptomundo, he places Spring Heeled Jack as the fifth most significant Flying Humanoid. In Ken Gerhard's book, Encounters with Flying Humanoids, and his article on Cryptomundo, he places Spring Heeled Jack as the fifth most significant Flying Humanoid. Gerhard described Spring Heeled Jack as... "So named because of his apparent ability to bound effortlessly through th