Kirk and Spock, daily, while telepathically linked, took mental journeys through crystalline realms of mathematical probabilities, or (if Jim was driving) to colorful fantasy worlds overrun with strange creatures. In their imaginations, they could travel through time, or live inside a favorite work of fiction.
Jim was addicted to Spock's unique, fantastically powerful way of communicating. It was more perfectly efficient than mere language, and there was an exhilarating intimacy that came with it. No secrets were possible between them. Jim loved that.
Spock loved it too. He hadn't played like this since he was a child in Amanda's lap.