Hot take: the "Pop Pop" in that old Rice Krispies jingle is not a sound, it's a nickname
Every ad nerd I know swears the three elves are just named after the noises, but in the 1930s radio spots they literally call the third one Pop, and the snap crackle pop is him answering to his own name, which somehow makes that 90 year old cereal jingle way weirder than it needs to be.
My grandpa used to do radio ads back in the day and he always said the same thing. The elves had real names in the scripts, Pop was short for Popsicle or something weird like that, and the whole "snap crackle pop" thing came later when they turned the names into sounds. Nobody believes me when I bring it up at parties. You just blew my mind with the 1930s detail though. That means kids listening back then thought they were hearing three little guys yelling their own names at people. Which is kind of creepy when you picture it.