Good, I take it that phrases with “to jest” are for some reason different than in “ty jestesz…”, where I need the instrumental, right? But what do you mean by “skip jest”? And where does this sentence have an object? I think in English one would call “big animal” a predicative noun or something like that.
I put ,,to jest duża zwierza" as my answer as that's what I heard in the example at normal speed. Slowing it down i can hear the "ę" sound a little better. It's come through as correct so I assume the difference is my answer would be specifically about a female animal whilst the "ę" answer would be inclusive of the male and neuter genders?