Norman Malcolm famously credits Sraffa with providing Ludwig Wittgenstein with the conceptual break that founded the Philosophical Investigations, by means of a rude gesture on Sraffa's part:
Wittgenstein was insisting that a proposition and that which it describes must have the same 'logical form', the same 'logical multiplicity'. Sraffa made a gesture, familiar to Neapolitans as meaning something like disgust or contempt, of brushing the underneath of his chin with an outward sweep of the finger-tips of one hand. And he asked: 'What is the logical form of that?'Thanks to the New York Times, here it is:
They translate it as "I don't care."