During the first century AD, many travelers crossing the deserts of North Africa used to take with them cockerels as a protection against Basilisk.
Strangely, a new type of Basilisk appears which had the head of a cock instead of that of a reptile. It was first called a Basil cock and later a Cockatrice or Cockatrix.
Its birth is very curious. It has to be born from a shell-less egg, which is laid by a seven-old-year cock during the period when Sirius the Dog Star can be seen in the sky. A toad or snake on a dung heap must then hatch the spherical egg. The cockatrice that emerges from the egg has eyes that resemble those of a toad but still retains their basilisk mortal stare.
To the medieval Christians it represented sin and sudden death.