This is one weird monster. It is difficult to make a rooster look ferocious. Now, don't misunderstand, a rooster can be a wicked creature. They are very aggressive and attack with wicked-hooked claws on their feet. They are related to the tyrannosaurs rex after all. However to take the head of one and put it on a serpents body is rather odd . . . . it is truly a beast of chaos.
The cockatrice is born when a rooster lays an egg and a toad sits the egg until it hatches. The beastly creature that emerges is evil, poisonous and able to turn you to stone.
These creature fist appears in the De Naturis Rerum in the 12th century by the acclaimed scholar Alexander Neckam.
This miniature goes a long way toward making it look pretty cool.