Basilisk (from the Greek "basilieus" meaning king, as in "king of snakes".)

 

Cock's eggs:
Its said that when a cock grows old, he lays a certain egg without any shell, instead its protected with a very thick layer of skin, which is able to withstand the force of any easy blow or fall. They say however that this egg is only layd in the summer time (between early July and early september).Its not very different from a hens egg, sometimes yellowish muddy color. And if a snake or a toad hatches the egg, it will bring forth a cockatrice.

Taken from "Encyclopedia of THINGS THAT NEVER WERE" by Michael Page and Robert Ingpen and from another web-site [link]  (only edited) 1