Wrathion's eyes flit sideways at the touch, warily skipping over Anduin then out over the water again.

To relieve tension.

His facial expression twitches, a faint tick of one muscle, then he sinks down another inch until his shoulders are completely submerged.

"Presumably the effect is not instant."

It isn't as if he wants to be on edge. Still, he can take a hint. Perhaps better to try and pack everything away, so that Anduin can at least relax himself. No need for Wrathion to drag them both down.