English often uses the article "a". You eat little "what"? "Little" acts as an adjective here without a object.
You also have to understand that duolingo is flawed in its very nature. They only use a single sentence, which can have multiple meanings, and they can only support so many responses when many more will work.
The bottom line is, if you can understand the nuance of the translation, then don't worry about alternatives that weren't included in the making of the translation. If you understand it, then it shouldn't matter. (It's not a video game after all. No points for U!)