The sad owl really does rule Duolingo...
Well, after more testing, it turns out that how it looks like when the owl cries in translations, you still get the points, is actually a display bug in Duolingo. Here's what happens:
You translate a sentence. The owl doesn't like it, because it thinks that hidrológico is an English word.
Looking at the Duolingo homepage, your daily coin stack just increased by ten points! They don't show up in your overall total, and it doesn't matter if the sentence was a 7-pointer or a 15-pointer. You "got" ten points. Yay!
Later, you come back and rate the owl's translation. No, Mr. Green Owl,
"mathematics may obtain numerical values from the equations elaborate and can provide a description of the developments that presents the tumor from the start."
is not a good translation. Downvote.
Going back to the homepage, your overall total just increased by one point, but your daily total went down by nine points. Turns out you didn't get any points from the sentence after all, only from rating.