“Bart, take a letter. Dear Mr. Burns, I’m so glad you enjoyed my son’s blood, and your card was just great.” – Homer Simpson
Liver spots are one of those undeniable signs of aging that remind us and others that the robust younger years are far in the past. Mr. Burns, being very far indeed from his days as a barefoot boy with cheek of tan, has quite a lot of them, something The Simpsons liked to have fun with, most famously when Marge catches Burns coming out of the shower in “Brush with Greatness”. There’s another liver spot joke in Season 2, however, that’s so subtle that I doubt I noticed it for years after I first saw it. In “Blood Feud”, Homer angrily dictates a letter to Burns after receiving only a lousy card in exchange for saving the old man’s life:
You are a senile, buck-toothed old mummy, with bony girls arms, and you smell like an elephant’s butt!
Later, after Burns reads the letter and decides to have Homer fired, he’s ranting to Smithers about the contents: 
Senile, eh? Buck-toothed, am I? Bony arms, are they? Liver spots, did I?
Notice the addition? Homer doesn’t mention the liver spots; Burns does. It’s the show taking a quick, barely perceptible potshot at Burns that you really have to be paying attention to catch. Burns doesn’t just have liver spots, despite his fearsome visage, he’s actually sensitive about them.
