It seems like this ordinary world is not enough for the genius, so their brains make new worlds and new scenarios (like "you get poisoned if you eat other people's food.")
I think they're super creative, and not just in science. In fact, they can come up with super intelligent methods for killing people, including themselves. That's why they're always paranoid, cause they think other people can come up with the same things to kill them.
After his wife couldn't make his food anymore, because he trusted only her.
Somehow I find that both sweet and tragic at the same time. That a man can be that paranoid and yet trust someone so completely.