Aeneid XII 865 se pestis ob ora

[Cinefactus]

Postquam aciēs videt Īliacās atque agmina Turnī,
ālitis in parvae subitam conlēcta figūram,
quae quondam in bustīs aut culminibus dēsertīs
nocte sedēns sērum canit importūna per umbrās,
hanc versa in faciem Turnī sē pestis ob ōra
fertque refertque sonāns clipeumque ēverberat alīs.

One of the books I have looked at changes the words to try to make sense,
pestis versa in hanc faciem sonans fertque refertque ad ora Turni
but I would have thought that in should go with faciem
I read it as:
having turned against the face of Turnus the plague both brings herself forward and back
but I can't make any sense of ob ora

Can anyone show me the error of my ways?

 

[Bitmap]

ora = face
facies = form/ shape
turned/ transformed into this form [the one of the bird just described], the plague turns herself again and again (se fert refertque) against Turnus' face (Turni ob ora; i.e. she flies around his face and molests him) and hits his shield with her wings.

 

[Cinefactus]

Thanks. I didn't realise you could use ob like that.