Feeding, proper feeding, always hit Stefan the same way, and there was a good chance that Damon knew it.
If he hadn't known before, he was certainly about to learn, there was a twitch that was almost a smile, Stefan wasn't as used to smirking as Damon was, but he was just as good at it.
What he let Damon see wasn't an emotion, really, and not really a sensation, but it was some tangle of both, so similar to the need for blood and vastly different at the same time.