Sherlock quirks an eyebrow. It's a good start. Not exactly the motion they need, but closer than before.

"Neat," he says, and means it.

"There's even a bit left," he says as he moves to reset the cups, lifting John's to show him.

"Can't have that." He gives a flick of the wrist, throwing the dregs of water up into the air before he sets he cup back down and refills it.

"Classroom isn't remotely soaked yet. Bit damp, if that. Not abnormal for a castle." Puddles and all. Sherlock returns to John's side.

"There. Do it again." So he can watch, learn the motion.