Sadly, in many bird species, newly hatched chicks are prone to commit siblicide, or the murder of their brothers and sisters for the sake of acquiring more resources. However, peregrine falcon siblings actually bond in a uniquely surprising way. Not only will they play with each other while airborne, but they will also practice their hunting skills on one another, where one falcon plays the role of predator and the other acts as prey.
CORRECTION: A previous version of this article stated that jellyfish are siphonophores. In fact, jellyfish belong to the phylum Cnidaria, though they are not siphonophores.