Noun
egg tooth (plural egg teeth)
(zoology) A small, sharp, cranial protuberance used by offspring to break or tear through the egg's surface during hatching.
The chick begins by "pipping"; pecking a breathing hole with its egg tooth towards the blunt end of the egg, usually on the upper side. Source: Internet
Hatching is an exhausting effort for the neonates, which break out of their eggshells with an egg tooth that falls off soon after. Source: Internet