Running out of hearts
There's a glitch I'd recommend fixing. When I run out of hearts in a lesson, the sad icon comes up immediately and the errors I made in the previous sentence aren't shown. I don't get a chance to see or learn from what I did wrong (as I do when making the mistakes that cost me the first two hearts).
You can click the link somewhere in the up-right corner of the screen with "Show your mistake" or something like that, right after you loose hearts!
Edit: "Show my answer".
I noticed that as well and just thought that for ages I was clicking too quickly!!
4arthur's point is that one is immediately kicked out of the lesson. I always click on show my mistake, but why should I have to? What serious language learner does not want to go back and understand the mistake?