Genjutsu works by manipulating chakra flow near spinal cord thus effecting ones five senses. In naruto characters have chakra pathway systems and this system acts as a circulatory system for chakra,disruption of its flow effects nearby organs as evidenced by neji vs hinata and gentle fist as a fighting style. That being said genjutsu doesnt work on those without a chakra system flowing to organs or people without a chakra system. This is evidenced by the dead being immune to infinite tsukyomi,the strongest genjutsu.
Trying to put anybody outside of naruto in genjutsu is like poisoning someones food without a stomach.
Trying to put anybody outside of naruto in genjutsu is like poisoning someones food without a stomach.