At the Krusty review when Homer is describing the pea soup, Lisa's pea soup appears/disappears between shots.
When Homer uses the viewing machine to see "The news from the day you were born" the headline about "an unusually large ugly baby" being born, if the joke is about Homer, strictly speaking that's impossible because newspaper headlines come the day after an event.
When Homer is writing his first review, Marge tells him there is no "e" on the typewriter, but when the editor reads his review he says that Homer used words as "pasghetti" and "screw Flanders", meaning that he did use the "e".
After see the cane from Citizen Kane, Lisa says that there was no cane in Citizen Kane. Actually, during the musical sequence "Is Charlie Kane", the singer have a cane.
A poster on the Italian restaurant's wall misspells the city name of Venezia as "Venizia."