Blood Feud

S2 E22: When Mr. Burns needs a blood transfusion, Homer is pleased to learn that Bart has the same rare blood type. Bart donates his blood and saves Burns, but Homer is upset to find that Burns sends him nothing more than a thank you note. Homer writes an angry letter in response, then thinks better of it, but discovers to his alarm that Bart has already mailed it. Homer tries to recover the letter, but fails, and a furious Burns reads the letter and vows revenge. But Smithers convinces Burns that the Simpsons have indeed done him a favor, and, in gratitude, Burns buys them a rare Olmec Indian Head. The Simpsons are unsure what to make of the gift.