Just a sly little look, a glance, a raise of those Vulcan eyebrows, and he knows what is wanted of him.
An order: "Spock, I'll speak to you in my quarters."
A knowing glance passes between the other crew members. The Captain and his First Officer think that they've hidden it so well, but to everyone else it is blatantly obvious.
The sedated walk to Kirk's room, showing no emotion, standing outside the door as if this was purely business.
The Captain catches up, and both know the logical outcome.
"Come, my love…"
And they are not seen for hours.