Severus pauses, and looks at him for a moment, not sure whether the riposte had really gone over his head or not. But it turns to a quirking mouth as Sirius turns to the kind of greed any Prince would be thoroughly in sympathy with. Wordlessly, he (neatly) severs the ribbons holding the parcel together, hands Sirius the book, does a quick reparo to stop his newspapers going everywhere on the way home, and settles into the book he'd picked up for himself.