The game says that Cloud was the only one during Hojo's experiments to show a response to the JENOVA cell injections. So, um, what WAS the response? Couldn't have anything to do with the semi-catatonic state he was in, since the people in black were messed up as well... the only thing I can think of that separates Cloud from everyone else is his ability to be controlled, but the files talking about Cloud being the only success were written way before that had ever happened. Meh...