Learn Croatian: Ne vjerujem svojim ušima: sto gostiju! - I can't believe my ears: a hundred guests!

In Croatian, when the object belongs to the subject of the sentence (in this case, the implied I), you use the reflexive possessive pronoun svoj, meaning one's own, instead of the standard possessive moj.

What case is svojim ušima, and what triggers it?

It is in the dative case. The verb vjerovati (to believe) requires the dative case for the person, animal, or thing that you are trusting or believing in.

The dictionary word for ear is uho. How does it become ušima?

The noun uho is neuter in the singular, but its plural form is highly irregular: it becomes the feminine noun uši. When you put uši into the dative plural, it takes the ending -ima, resulting in ušima.

Why is the word for guests gostiju rather than the standard plural gosti?

Numbers from five and up, including sto (a hundred), always require the following noun to be in the genitive plural case. The noun gost is also slightly irregular here; instead of the usual genitive plural ending -a, it takes the special ending -iju, making it gostiju.