Elephants have a fission fusion society in which multiple family groups come together to socialise.

Another fissile isotope, uranium 233, can be produced from natural thorium and is also important in nuclear technology.

A letter from Bohr, commenting on the fact that the amount of energy released when he bombarded uranium atoms was far larger than had been predicted by calculations based on a non fissile core, had sparked the above inspiration in December 1938.