Wow dude, I posted the definition of flesh twice in this thread.....
Bijuu are entities that can survive without any organs or flesh. They are purely made up of chakra, yet they live. But if you want another example okay then. How about oro and kabuto? remember when kabuto implanted some of oro's chakra into himself? kabuto said that oro was slowly trying to take over, even though kabuto had full control. Now tell me how can oro, who is purely made up of chakra at this point, possibly take over someone if he doesnt have a brain? Or better yet, how was oro able to get revived from anko's CM? he was just pure chakra at that point?
Wrong, bijuu are controlled via the sharingan, becuase there is a long history of eyes controlling beasts. Genjutsu doesnt work on bijuu, but you can control them with the mangekyo (same with mokuton)