maybe (and this is just a wild assertion from be being too happy today) sasuke chidoris naruto right through the belly...on the seal. in a last ditch effort to survive the kyuubi heals nartuo. then the seal fizzles and naruto goes back to normal mode. then sasuke gets pissed off that he wasted his last chidori and goes level 2.
yeah...i know ...its lame

btw, if naruto gets impaled anywhere by the chdori, then im convinced that nejis alive.