I think there’s a lot of unspoken hurt behind a magician’s voice when he says, “Look, there’s nothing up my sleeves.” It seems to suggest that, at one time, magicians were free to keep loads of stuff up their sleeves: coins, cards, dice, maybe even mulled wine and fresh apples.
Then, one day, some novice magician reaches just too far for the salt, causing all his sleeve-ware to spill out, and suddenly the gig is up. From then on, magicians around the world have to assure their audience that nothing, absolutely nothing, is kept up their sleeves. In fact, a whole cultural turn-of-phrase develops around the ordeal, painting magicians as thieves, charlatans, and swindlers instead of talented entertainers.
They still perform their illusions, but a tiny part of every magician dies with the words, “There’s nothing up my sleeve.”