"You eat duck."
Translation:Εσύ τρως τις πάπιες.
Because I think that in English, when you refer to animal meat, you use singular instead of plural. For example, "Do you eat pork?", "Do you eat beef?", "Do you eat chicken?" etc. Which is also the case in Greek, but plural is sometimes used as well. It does seem a bit odd here, but it's not wrong. :S
But if singular is also correct, it's too confusing for Duolingo to teach plural here, unless it's very, very, standard, common usage in highly populated areas of Greece (not just "sometimes".) (Google translate doesn't offer the plural in some sample sentences I tried.) Now that I've written this I'll probably remember πάπεις without even cheating, but only for these lessons.