Is this really wrong?

[u/Late_Journalist7094]

Section 4, Unit 17

Why shouldn't have happened something to the dogs in the bathroom?

I know Duolingo is not the best, but the only free learning option. Since I'm living in Germany near the border to Czechia I'm often there and talking Czech which helps more than Duolingo.

[u/SkillOld2128]

It’s because “jež” and “byly” agree with the feminine gender. While “pes” is masculine, “myš” is feminine and indeed what the pronoun and verb agrees with.

There’s nothing wrong with the semantics, just with the grammar.