"I am not a horse." Translation: Yo no soy un caballo.
I have come to the Discussion to submit this as a Free Write Report in the hopes that someone with authority will read this and respond or pass it on to the Report Section of Duolingo. I have been a member for several years. I recently encountered this sentence in the Animals section of the course. On the Discuss page associated with this sentence 90 members have written "No soy un caballo." as the answer and had it marked wrong. I do not know how many of those submitted a Report marking the "My answer should be accepted". option. I wrote the same answer as the other 90 members and submitted a report today, April 23, 2018. If we are all wrong in thinking this is a correct answer, please have someone reply on the Discuss page of the sentence and explain why it can only be: Yo no soy un caballo. Gracias por tu attención.
Concuerdo contigo: No eres un caballo.
I think the sentence without the pronoun is perfectly OK. I once learned that in Spanish, it is even more common to leave out the pronoun.
I can understand that Duolingo uses the sentences with pronoun in order to make it clear to us which person the sentence refers to. But it should certainly allow the sentences without the pronoun in our replies.
(Just my two cents as a native speaker of German. :-))
No soy un caballo or No yo soy un caballo. The only reason you may put Yo , no soy un caballo is if you are responding to a statement made to you by another. This would emphasize your reaction I .. I am not a horse. Now back to No soy un caballo and No yo soy un caballo. Both are correct. But there is no need to put (yo) in the sentence un less you are strongly stating it.AS to strongly stress that you are not a horse.