Quote Originally Posted by XanBcoo
At the time I took it to mean that Shukaku was the spirit of the Sand Priest, sealed and then attached to Gaara.
I thought that then, too. In fact, I've always thought that bijuu "grow where hatred festers", like Gaara's attendent said (I think). I thought that was the best part of the Gaara story -- when we found out that the priestess that was sacrificed was his mom. So it makes sense that a human sacrifice could turn into a monster. If we entirely ignore the Jyuubi, it makes sense that Sasuke's hatred is growing and turning into Susanoo-bi.

But Kishimoto has shifted gears since the time jump. "Growing where hatred festers" is too generic in a world with guys like Pein around.