Dexter's Laboratory (1996)

S1E27 The Big Cheese

Dexter invents a gadget that lets him absorb knowledge for his French test while he sleeps. However, the device goes haywire, causing the phrase "omelette du fromage" to echo in his mind all night. When he wakes up the next day, he finds that he can only say "omelette du fromage" and nothing else.