"The ducks do not eat the plates."
Translation:Ankorna äter inte tallrikarna.
There had been tension between the ducks and the plates for a while. The ducks had just been sitting on the lake, and as the humans came to give them bread, they bring out their own food... on plates. The ducks cannot help noticing that the plates did not move for a while. But suddenly, there is a gust of wind and before the humans can get up to notice, the plates are coming after them. They're tired of holding so much food and need some food for themselves. So they go for the ducks. The ducks could fight back, but they are on a diet, so the ducks do not eat the plates. Instead, the plates eat them. (They are in Soviet Russia.)
ej is still used but it's considered formal. It's also good for situations where brevity is important, so you'll see it on e.g. street signs and similar.
It's a very common word so it's important to accept it, but unfortunately Duolingo doesn't have an option to "accept this, but don't show it to learners unless they actually enter it". So the system displays it to users now and then when they get something wrong, even though it's never the default.