[ As he turns back around his answer is flippant, almost unnervingly so. ]

'Cuz I lied. Your technique is fine. But yer' not like to summon a Patronus while on the brink of a temper tantrum with that famous Wayne temper, hey?

[ Because the child isn't the only one who can do precision-strike callouts. Besides, if he's busy meditating he might not notice when John starts his summoning. ]