All Our Yesterdays, which makes no fucking sense whatsoever - if travelling back 5000 years makes Spock suddenly like a Vulcan from those times, when he isn't from those times, why aren't Kirk and Bones suddenly speaking... Pictish or something?
I always thought that Zarabeth simply set feelings in motion that he didn't get to "take care of" during his pon farr in "Amok Time". Never bought that he was acting like Vulcans from that time.
Though if he could feel the deaths of the Intrepid
crew in "The Immunity Syndrome", couldn't it be possible that all those raging Vulcans could be having some type of effect via telepathy?