"The cat plays with the thread."
Translation:La kato ludas per la fadeno.
I'm not sure what that implies, but I fear that in this and other Duolingo courses, if enough people report a certain answer as "My answer should be accepted", then it sometimes gets added just to keep them quiet, whether or not it really should be. I hope that is not actually the case.
My only point was that "the course accepts it" doesn't always mean "the answer is correct" - especially in the light of the other conversation in this thread. For what it's worth, I really don't know whether the course accepts it.
There are mistakes in the course, but they are rare. There are also situations where the course accepts common misspellings (e.g. cloths for clothes) not so much to "keep people quiet" but to avoid needless frustration not related to learning Esperanto.