You should not prefer זה to הוא even in those other excercises. In formal Hebrew one uses only הוא, while זה would be considered inappropriate; in spoken Hebrew both sound fine (I guess I would tend to say הוא, but not sure).
Agree, in plural it's less appealing, though still sometimes OK, to say אלה. A safer bet is always הם or הן.
ארנב ונחש הם שניהם חיות The odd feeling you get is ultimately related to the fact that Hebrew doesn´t have an indefinite article thus the singular has more of a tendency to represent the species (as opposed to English where the singular without an article represents the product of the animal as in "rabit and snake make good pelts")
Not odd in Hebrew, I have no doubt every Hebrew word and sentence in this course is accurate, but the problem lies with the English translations. Your above explanation about "rabbit and snake make good pelts" made perfect sense. The problem I've been having, as an English speaker trying to learn Hebrew from scratch, is that when the English translations are odd, I'm not sure if it's because the translations themselves are inaccurate, i.e. made with typos, or are as close to literal as possible. "A rabbit and snake are animals" must be a typo. Either both animals should have indefinite articles, "A rabbit and a snake" , no articles (referring to your pelt explanation) "Rabbit and snake", or they should both be plural "Rabbits and snakes."
My feeling from Duolingo in general is that they usually opt for the closest translation possible, word order and form wise as opposed to exact semantic meaning, which is indeed sometimes not a good natural translation of the concept, but its just a tendency and sometimes it goes the other way.
I found this too - with the picture options. Since the box doesn't say "Type in Hebrew", the Duolingo keyboard doesn't activate.
The only way I found was to switch my PC keyboard from English to Hebrew for that answer (i.e. the way I had to type in Hebrew before I started using the Duolingo keyboard).
Having similar problems. My keyboard worked perfectly until I cleared out all my browsing data and cookies. Then it only wrote English. I can't work out a way to deal with the problem properly but at a later date when I cleared the browser but not cookies my keyboard suddenly started writing in Hebrew again... all the time! Now if I want to type an English answer I have to write in capitals. It's much better than no Hebrew at all but a little strange. Anyway my point is clearing your browser history may improve the situation and if you find a proper fix please let me know.
I think it's correct, but a bit stretched... הם is a personal pronoun ("they"), but also a copula ("are"), and in this Hebrew sentence it's much more naturally to interpret it as a copula. Your English suggestion is kind of like two sentences, "rabbit and snake (pause) - they are animals" - I'd use the same Hebrew words for this, but it's a much less natural reading.