In the interview, Kelley commented on the character development of Dr. McCoy from film to film, as opposed to the incremental changes he worked on during a weekly TV series.
Notably, he said, Dr. McCoy had mellowed out a lot. In the series, McCoy was openly annoyed by Spock's cold logic, but that relationship had to evolve.
Kelley didn’t want to soften McCoy, but he wanted him to “become a little more attuned to Spock.” He had McCoy view Spock with more amusement than irritation.