Doing as he's told brings him its own rewards. First of all, what he's told to do so happens to be something he immensely enjoys doing —the struggling, straining, feeling the rope tight and rough around his wrists—, and secondly, what Spock gives him is exactly what he asked for, and then some.

Jim barely has the time to react, a surprised gasp leaving him, then being choked out of him when Spock's hand tightens. No sounds slip past his lips now, not when he can't even draw a thread of air into his lungs. The grip is careful but tight and strong, and Jim's head feels considerably lighter with each passing second, his very skin burning hot as he struggles pointlessly again.

He can't move, just like he can't breathe. His eyes are dark as they settle on Spock, looking unfocused, but he doesn't even try to shake his head, though he does act like he tries to speak. He can't, obviously, a fact that only arouses him further. His hips shift again, grinding just barely against Spock's, trembling from head to toe at the onslaught of pleasure that washes all across his body.