Sometimes at dusk when i sit on my balcony, i see a bat whirling around the appletree. One time s/he flew really close by and i heard the sound of the wings : db.db.db.db.db. Then i realized the old Kiëngiric/Sumerian dubdubu is an onomatopoeia!
(Actually the word is dubdubumusen , musen being a determinative meaning 'bird'. Other determinatives e.g. : dingir =god/goddess, gis =wood and na =stone (Nice example : esi=hard , gisesi=ebony naesi =diorite )