During embryonic development, on the 6th-7th day of incubation, the chick develops a horny protuberance on the tip of the beak (upper rhamphotheca). This protuberance is called egg tooth, generally translated as “egg tooth” or “little tooth” or “diamond”. The function of this protuberance is to allow the chick to break the shell during hatching.
The egg tooth usually falls off the day after hatching, although it is not uncommon to observe chicks that lose the protuberance after a week or ten days.