Alice played Swindler, Bob played Caravan Guard in response, so he drew a card. This changed the top card of his deck, so that when Alice's Swindler hit it trashed his Peddler, and since the Peddler pile was empty he gained a Province. In response, Carol revealed Fool's Gold, gaining the last Gold in the supply on top of her deck. Alice's Swindler then trashed that Gold, but there was nothing for her to gain in return.