Nursery song refrain

EIEIO

Think of the sound a farmer might hear while tending to animals in a classic children’s tune.

This clue points to the famous refrain from the children’s song "Old MacDonald Had a Farm," where the repeated line ends with "E-I-E-I-O." The answer is spelled exactly as it sounds in the song, capturing the playful, sing-song rhythm kids love. It’s a direct reference to a well-known nursery rhyme, so no tricky wordplay—just pure musical nostalgia.