His reaction is vocal-- a brief exclamation that is significantly louder than any he has made up to this point (he has not been completely silent, of course, but he certainly has not been making a lot of noise for what he is doing). The feeling of her contractions quickly sends him over the edge and the pressure releases itself all at once, exploding into her in a manner that she can possibly feel.

Oblivion is one way of putting it. Sweet, definitely. Technically what registers with his systems is a brief power surge that renders several of his cognitive functions temporarily offline, as his neural network attempts to process the information, the amount of feedback which is now streaming back and forth between his senses and his emotional programming as a result of those new connections.

But the technical description is nothing next to what it feels like.

The sensation is nothing short of overwhelming.

His head twitches from the base of his neck; his entire body tenses, then shakes. He lets go of her and tries to brace himself on the mattress and the headboard, worried that he might be exerting too much force onto her.

He tries to slow his breath, then, but his systems are only allowing him so much control. He bites his lip, and moans a little at the slight pain he was not expecting. But the sensations slowly become less overwhelming, and he is able to dedicate more processes towards visual information-- he sees River now, looks into her eyes in this moment. But he is overwhelmed again, and he closes his eyes, turning away slightly. In fact, he is a little ashamed.

He has started to cry.