Listen: Baby crocodiles stuck inside eggs talk to each other
The pre-hatching calls of baby Nile crocodiles actually mean something to their siblings and to their mothers. The calls -- which are perfectly audible to humans and sound like "umph! umph! umph!" -- tell the others in the nest that it's time to hatch, according to research in Current Biology. Those cries also tell the mother crocodile to start digging up the nest.