"Those foxes are eating a duck or a goose."

Translation: Ty lišky žerou kachnu nebo husu.

[Helenagvtierrez]

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

[VladaFu]

It is the accusative case. See the Tips and notes.

And do not put the "a" there.

[busibody]

Why is it "ty" and not "ti"? I thought lisky was nominative since it is the subject of the sentence.

[BoneheadBass]

It is ty because liška is feminine and, yes, it is in the nominative. Ti would be used with a masculine animate noun.