Parlor tricks of the mind and a life of leisure allow for certain mental tools to flourish, rather than be vestigialized.
Eight digit mental multiplication isn't a difficult feat. All it requires is you to be able to hold 16 digits in your head. Or more easily, 4 chunks of 4 digits. If you practice and focus on it, you too can relearn how to do long mental arithmetic. But this also requires you're still able to "relax" and empty your mind like a child's, rather than be constricted into an adult's neurotic "I must always be doing something."
Holding conversations in multiple languages? Many bilingual children could join von Neumann, if their parents were as wealthy and involved. Wealth must be present; not only because physical resources give way to access to better tutors and learning material, but also to a tranquility of the mind and soul, that is not found anywhere else but the leisure class (i.e. if you're an upper middle class parent trying to "push" your child into enriching endeavors, all you're teaching is mechanical skill, at the cost of your child's creativity and individual expression -- their soul. Something I've seen too many times).
This is also why anyone who's been in the corporate world for too long, is forever locked out of any great creative or mental achievements: the mental tools needed have atrophied, and it simply is unlikely you'll be able to retrain them, unless some drastic lifestyle change happens (or you do just the right amount of drugs, another improbability).
t. Someone that could also do very long mental arithmetic and "hold conversations" in multiple languages at
6. Going from upper class to being a prole, due to a certain ideological group, has left me painly aware of all the things I've lost. Pieces of the mind and soul that are locked away from the rest; all due to economic circumstance.