This is the 12721st most frequent Russian word.
кошками
"Кошками" means "cats" in the instrumental plural form in Russian.
In this sentence, 'кошками' (by cats) is used in the prepositional case to denote the subject of interest.
Маша всегда интересуется кошками и читает книги о них.
Masha is always interested in cats and reads books about them.
Here, 'кошками' (with cats) is used in the instrumental case to indicate the instrument by which the action was done.
Они были окружены кошками на улице.
They were surrounded by cats on the street.
In this sentence, 'кошками' (about our cats) is instrumental to denote the medium of exchange.