Why are the strength bars going down so fast?
I don't know. It just seems really weird. Should it going that fast? Like, I was almost 1/2 down on animals 1 and I knew all of them.
Don't bother about the strength bars. And the fluency % is very unreliable. There are many complaints about this behaviour of Duolingo, since Duolingo's staff stopped an A/B test for Fluency and started the new web version recently.