I apologize in advance if this makes so sense whatsoever.
Me, my mother, and my brother watched Wrath of Khan and Search For Spock last night and we questioned why Spock chose Bones to carry his katra, or soul, in. The answer was simple. Bones has no soul.
Plenty of room for Spock to sit comfortably until he got his body back.
And of course, Bones is none to pleased to hear that he has no soul, arguing commences....who will win?
PART 2!!!!! [link]