Nagging Thoughts is a common Sorcery card from Shadows over Innistrad (SOI), collector number 74. Current market price: $0.07 (foil $0.19), TCGplayer market prices via Scryfall.
Look at the top two cards of your library. Put one of them into your hand and the other into your graveyard. Madness {1}{U} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)