probably a flexatone kinda like a boing sound? roger and zapp used it alot too? If so thats a flexatone its a real instrument, its a dual forked pitched metal rod with like a rubber ball in the middle secured by elastic or something. i never saw one in real life only pictures, i'd love to get my hands on one though it would definatly come in handy
look it up on google images to see what it looks like. its like i described but theres like a metal plate behind the fork and there is two balls (lol 2 balls)