Flashcards are used to quickly practice words previously learned on Duolingo. Users grade themselves as they are shown words in the language being learned and their translations. This replaces the "Practice weakest words" button, which had functionality identical to the strengthen skills button on the home page. As of May 2015 these flashcards are currently unavailable in some courses . Duolingo also offers tinycards which has a similar feature set.
Practicing with flashcards strengthens words, but the "decay rate on words that you mark wrong, however, is much higher than for the words that you mark right. This means the words you didn't know will lose their strength faster over time than the words that you did know, even if they are initially bumped up to the same strength."
Flashcards are different from normal practice: