ty lisky zerou a kachna nebo husu. this was my answer and i don't understand the difference it makes if i say kachNU or kachNA
It is the accusative case. See the Tips and notes.
And do not put the "a" there.
Why is it "ty" and not "ti"? I thought lisky was nominative since it is the subject of the sentence.
It is ty because liška is feminine and, yes, it is in the nominative. Ti would be used with a masculine animate noun.