Originally posted by: Jessper
Well, you don't generally remember anything from your childhood until you are older so it is pretty unreasonable to think that he would remember the attack. Also the "fox-shaped chakra" only has one tail, nothing like the nine-tails we hear about all the time. Finally since we can assume that he had no memory of the fox's attack why would he even begin to think that he has the fox in him?
The way movies and anime work usually is that the viewer has more information than certain characters. To think the clueless person should do something or realize something when they have no inkling of what is going is asking for huge plot holes.