Then there must be a bug in here - when you get it wrong, the system gives 'Where is the arse' as the correction. Arse is fairly vulgar British English for zadek!
Však to tak je. To arse si vymýšlí samo Duolingo, jako automatický ekvivalent každého ass, asi jim to přijde nějak užitečné.
Well, "osel" is quite often used as an insult for people, so even if you do not use it yourself, it is good to know it, in case someone calls you that. :)
Difference between Osel and Osla? I cant get the extra help to work on my computer