Blood Feud is the twenty-second and final episode of Season 2. It was originally broadcast on Fox in July 11, 1991. The episode was written by George Meyer and directed David Silverman. The episode includes the debut of the Olmec head Xtapolapocetl, which would become a common background prop in the Simpson home. It features several reference to the movie, Citizen Kane, and songs such as "Iron Man" by Black Sabbath.
Homer discovers that Bart has a rare blood type that can save Mr. Burns' life, Homer convinces Bart to give blood (in the hopes that Burns will give the Simpsons a cash reward), but when all Mr. Burns gives Bart is a "Thank You" card, Homer writes a nasty letter to his boss...which ends up getting sent to Burns by Bart.
When Mr. Burns falls ill and desperately needs a blood transfusion, Homer discovers Bart has Mr. Burns' rare blood type (double O negative), and Homer urges his son to donate, promising that they will be handsomely rewarded. However, Mr. Burns knows nothing of this promise, or even of the Simpsons' desire for a reward, and having received the blood, all he does is send the family a card. Enraged, Homer writes an insulting reply, but Marge convinces him at the last minute not to send it. Later the letter goes missing, as Bart has mailed it still thinking its message is called for.
Homer and Bart's attempts to stop the mail delivery ends in failure, and Mr. Burns is furious at the insult and demands that Homer be beaten. Waylon Smithers calls off the beating, however, on the grounds that this action is no way to thank the man who saved Mr. Burns' life. Just as Marge had convinced Homer to refrain from sending the letter, Smithers has a calming influence on Mr. Burns, and the two men decide instead to buy the family a present. The Simpsons receive an antique, an Olmec head (a massive, Tiki-god-like affair) of Xtapolapocetl (Pronounced 'Ex-tapo-lapo-kettle'). Bart, the blood donor, likes the gift; while Homer hates it.