Too much repetition ?
As I have already suggested in "Feedback", I think there is too much repetition and not enough revision of former vocabulary. To keep us on our toes, surely it would be easy to insert two random exercises from earlier lessons?
The problem is that in the "Spanish Tree" all the answers touch upon the same kind of questions and are therefore too predictable. My point is that random questions from previous lessons would force useful revision.
While you are logged in, click on the vocab tab. Or go here http://duolingo.com/#/vocab
Both bring you to the same page. A solution for some of your issues. If that's not entirely an answer, simply go back to the areas (on your spanish tree) you'd like to touch up on.
If neither of those help, then the owl cries with you. :P
If you click the "practice" blue circular button on the left side of the page, you can practice previously learned material. You can choose how much you want to review and how much you want to learn something new by choosing the number of times you click the "practice" button and now many times you work on the lessons.