Unintentionally "peeking" at words
When a new word is introduced, you usually have to mouse over to see the meaning. If you then use "enter" to get to the next page, your cursor stays where it is, which results in you "peeking" at the next word that appears in the same spot, even if you didn't need a hint for that word.
If "peeking" is being tracked to give Duolingo an idea of which words are most difficult for you or that you need to practice more, then it's not good for accidental peeking to affect that. (Perhaps this explains why some of the same sentences recur for me over and over even though I now know them by heart?)
Maybe it could be changed so that when you advance to a new page, the mouseover hints don't come up unless you move the cursor off the word and back again? This seems like a small alteration (as far as I know; I'm not a programmer) that would greatly improve the quality of my experience on the site :)
I'm using Google Chrome, by the way, in case it's a browser issue.
It's just a matter of deactivating the mouseover event. In short, every mouseover event must be preceeded by mouseout.
One way to do this is to have a flag that shows whether the event is active. By default it is true. At the end of each mouseover event it is set to false. When mouseout event is triggered, the flag is set to true again. When triggered, the mouseover handler just returns if the flag is false.
The other way is to remove the event handler on mouseover and add it again on mouseout.
Lots of times I have accidentally triggered the peeking popup which I just ignored. However now I have read that Duolingo uses said peeking as a statistical basis for categorizing students progress on individual words as well as aspects of the overall program.
If Duolingo regards such peeking as important perhaps they should devote some attention to ensuring peeking hits are a valid signal and not just noise. Not sure how they could or should do it but I hate to think of everything being thrown out of whack because of my clumsy mouse movements.
Okay, as I said in a reply comment, what if they have the first mouse-over display a separate message that says "Mouse over this word again to peek at the definition" or just "Mouse over again to peek", and if they take the mouse off and move it back on again, the message would change to the actual definition of that word, and then fire the "You peeked" subroutine, whatever that may be.
Just a thought.