They have sonic sound!
Did they go “zzzip” when they moved?
Did they go “bopp” when they stopped?
Did they go “brrr” when they stood still?
Exactly what I was thinking. For those not in the know, here’s “The Marvelous Toy,” by Peter, Paul, and Mary:
That confused the hell out of me when I was a sprog, and when I got older I figured I’d misremembered it because “sonic sound” is bad and would never make it into a commercial.
Mt brother had that. One of the few toys I remember that genuinely did what it said on the tin, worked effortlessly, and were loads of fun.