And then he recovers the pebble from where he'd concealed it, up his sleeve. Then: he repeats the trick, half speed. An arch of his eyebrows is the warning she gets before he does his trick: the pebble tucked almost invisibly into the fold between pinky and ring finger, then dropped into the gap between wrist and sleeve. Then, to complete the trick, he lifts the first shell, then the second - and then flicks the pebble under the third shell as he lifts it up, so that it looks for all intents and purposes as though it had been there all along.