I realised that match madness, matching words as fast as possible, helped me very rapidly to grow my vocabulary in a robust way. I love this aspect of Duolingo but the problem for me is that the 'learned words' section of the app feels really basic. To review words I know there's a matching exercise, but even when I perform that exercise 10 times in a row, the words I'm asked to match don't seem to get more complex. 9 times out of 10 I'm asked to work on the same very basic words that I already know very well, while my actual list of known words is way bigger and filled with things I'd like to work on and familiarise myself with. 1 time out of 10 some other lesser known stuff from my words list appears, but afterwards we are back to the really easy stuff that I've seen enough of. In my opinion the word matching section of the app should grow in difficulty if the user is spamming it - I would find that immensely helpful! Thanks :)