Spock's Katra *spoilers*
Spoiler tag is probably unnecessary at this point, but better safe than sorry I suppose.
Anyway, at the end, Spock transfers is Katra (sp?) into McCoy as is explained more fully in the next movie. It got me to thinking, were there times in the original series that Spock was in a life threatening situation and it might have been a good idea for him to have done so?
I'm not recalling any off the top of my head, but I'm sure there were times Spock faced almost certain death and maybe should have thought to do so.