The legendary actor talks a pivotal scene in The Naked Time original series episode.

"It was a very fertile period and the directors were open to ideas and and Bill Shatner, myself and Deforest Kelly offering came up with character touches and character ideas and seeing ideas. That were helpful.  It was a scene that was not in the original script and I asked for that seemed to be written. I think it's it's a chance to really reveal what the Interior was Spock.So they wrote it for me .It was late. One day almost at wrapped time, they just have one crack at this and then we have to wrap so we did it quickly but I turned out to be quite effective and and shortly after that episode went on the air, fan mail for Spock exploded."