I heard this in a Japanese song sung by Vocaloid Hatsune Miku (YouTube)
Does anyone know what this onomatopoeia means? It's clear from the context of the lyrics that it is an onomatopoeia, but I've never heard it used before.
For context, the lyrics say:
I’ll puff out my cheeks and go
“mokyu mokyu” just for you, OK?
I’ll make duck lips and go
“mokyu mokyu” just for you, OK！