"Your horse eats salt."
Translation:Το άλογό σου τρώει αλάτι.
While I hope someone can clarify this too, I've noticed it has got the double accent whenever the horse is his /hers/ theirs/ yours. So I'm guessing it's a rule to do with the flow of a sentence. Perhaps it says more in the tip section.
It has been a while since I've seen this, which lesson does it belong to?
"So I'm guessing it's a rule to do with the flow of a sentence."
Something like that. I think it has to do with the pattern of stressed and unstressed syllables. It was mentioned in passing in my Koine Greek class a number of years ago, but not really explained. (We mostly ignored accents, except where necessary to distinguish between words like ο and ό.) And since the Duolingo mobile app never explains anything, I haven't a clue what the actual rule is.