Sephiroth: Cloud, after you kill me, I will come back you know.
Cloud: But how?
Sephiroth: ... Life Materia.
Cloud: WTF?!?!
Sephiroth: Yes, Cloud. That is why I live for so long.
Cloud: Then I'll destroy all the life materia.
Later...
Cloud: I'm done.
Sora: Umm, Cloud?
Cloud: Hm?
Sora: Sephiroth just killed Aerith again.
Cloud: S**t