I tried my best to find the Ancient Greek word for ow. In Aristophanes's Θεσμοφο�?ιάζουσαι (Thesmophoriazusae = Women celebrating Thesmophoria) it is ωι (cf. here, end of page 21), but unfortunately it lacks diacritics.
Which of course is something that actually happens in certain versions of Cinderella: the stepmother hacks off one of her daughters' heels in a vain attempt to make her fit the slipper. What's Greek for "ow"?