Thought Rattle is a rare Sorcery card from Alchemy: Bloomburrow (YBLB), collector number 30.
Target opponent reveals each nonland card in their hand. You choose one of those cards. Exile that card. Threshold — If seven or more cards are in your graveyard, seek a Rat card. It perpetually gains "This spell costs {1} less to cast." You gain 1 life for each Rat card in your hand.