When I tap on the word "zwierzętach" in this sentence, I really wish Duolingo would generally not only show the translation but also in which case this word is written and also what the nominative of this word is. I often see a declined noun and have no clue what the "original" word is and why it is declined in this way...kind of frustrating...
Do not get misguided by the name of the case. This is exactly what locative in Polish is used for (not only, though). In many declension tables of Polish words it is even predefined with the preposition "o".
In Polish you use locative every time when the phrase means "in the subject of". It is not only to express a physical location, but also so to say, "location of interest". It is used when you can answer to questions:
w kim? - in/with/from who/whom?
w czym? - in/inside what?
o kim? - on/about/of who/whom?
o czym? - on/about/of what?
- Książka o zwierzętach (Loc.) - A book about animals
- Konferencja o zagrożeniach (Loc.) - A conference on threats
- Myślę o tobie (Loc.) - I think about you
- On mówi o tej książce (Loc. x2) - He is talking about that book
- Jestem w domu (Loc.) - I am at home
- Kot jest w pudełku (Loc.) - The cat is in the box
- Zakochałem się w tobie (Loc.) - I have fallen in love with you
- Mam w moim synu (Loc. x2) podporę - "I have support in my son", my son is my support
- W Bogu (Loc.) (jest) nasze zaufanie - In God we trust
Dear Friends, to get clear sense of what and why Locative case is used in polish, please read a wikipedia page here: https://en.wikibooks.org/wiki/Polish/Locative_case