You should give this duck a name. I beginning to feel this creature will accompany us throughout all the lessons. Soon we'll know its habits as well as our own pets.
First of all, I'm not really sure what that would mean... Second of all, as far as I know, when talking about a person/animal you don't say ישן for old, you'd say זקן. I believe ישן is used for objects... Third of all, in this sentence, the word ישן is pronounced "yashen" which means sleep. To say "old" you'd need to say ישן with the nikkudot so that it's pronounced "yashan". I'm not sure how Duo expects us to know what nikkudot it intends, though, unless we're just supposed to infer it from the context (which can sometimes be difficult because sometimes Duo gives silly sentences that you'd really never use....) I apologize if I wasn't so clear, this is hard to explain... Good luck!