"This one is my long sword."
Translation:Kesy ñuha korze issa.
despite "bisy" being another alternate for "this one", using it made the answer invalid thanks duolingo i want death
"Bisy" (and "Bony") is for animate objects, so mostly animals and people, while you use "Kesy" (and "Kony") for inanimate objects instead. You can't choose one or another, there is a clear rule for when you have to use one and not the other.
"Korze" is clearly inanimate, so "Bisy" would be wrong in this case.