That of eavesdropping beyond the shell is a skill that many animal embryos use to survive. Even chicken eggs listen to what you say.
It's true: chicken eggs listen to us. And they listen not only to the song or words of humans, but to all sound stimuli around them. Contrary to what you might think, for the animal cell interpreting acoustic signals is not a quirk, but a way to adapt and survive.
Although the most striking example of an embryo "with ears stretched out" is precisely the egg that many of us probably keep in the refrigerator (but at that point is not really likely to hatch), these early auditory capabilities are common to other creatures of the animal world: and not only when they are inside the shell, but also when they are still in the mother's womb.
The discovery about the female gametic, or sex, cell of chickens dates back to 1967, when research published in the scientific journal Science succeeded in demonstrating that chick embryos were able to listen to, interpret and memorize the noises of the outside world.
What we know about eggs that hear us
Similar research has been extended by scholars to bugs or tree frogs, among other animals. In fact, the embryos of both species seem to be able to adapt to survival precisely thanks to sounds.
Bugs, for example, use the noises produced by other individuals in the brood to coordinate the breaking of the shell and to be born all at the same time. Tree frogs interpret sounds produced by an approaching predator as a signal to pierce the shell and escape a dangerous egg-eater.
The Surprising Example of Australia's Zebra Finches
Mylene Mariette, author of a study published in the scientific journal Trends in Ecology and Evolution and a behavioral ecologist at Deakin University in Geelong, Australia, has collected a good number of studies on animal behavior before birth.
Firsthand, she then contributed some observations on the Chestnut-eared Fringillid, also known as the Zebra Finch. This species of bird, which has adapted to living in the Australian desert, wheezes, as dogs do, to cool itself during particularly hot days. This behavior certainly does not go unnoticed, to the point that, in some areas, it is possible to hear the little creatures produce the typical cry associated with the heat.
About eggs, Mariette discovered that on the other side of the shell, there are those who listen to the chirping of the panting Zebra Finches, using this input as a kind of thermometer-spy that gives the sign of very sultry days, otherwise undetectable by the embryos being hatched.
In the long term, finches that have received the sound input of chirps will tend to grow more slowly, a development more functional to survive in a hot climate. According to the observations of the researchers, they would also present brighter colors.
Other sui generis characteristics, always associated with the animal world, can for example be found in the ant that does not age or in the immortal jellyfish.