"The cat's men."
Translation:Fir an chait.
That sounds like an issue with the functionality of whatever version of Duolingo you are using - take a screenshot that demonstrates the problem, and submit a bug report with the screenshot and a detailed description of the version of Duolingo that you are using (iphone app, android app, website, the web browser you use, etc). The people that are in a position to fix bugs in Duolingo don't read Sentence Discussions, and your comment in a sentence discussion will never be acted on.
If i understand, "cat" is lenited because of the genitive form, yes? So then i thought it'd be "chat" not "chait." Is the genitive here plural for singular? (My apologies if the question is unclear, realizing i don't know the name for the rule being applied here, so not sure where to look it up.)