'den Hund' is the accusative form of 'der Hund' (the dog). When a masculine noun (for example 'der Hund') is the object in a sentence the article 'der' changes to 'den'. 'Die Kuh hört den Hund', 'Ich trinkt den Tee', 'Ich siehe den Junge' and 'Sie essen den Salz'. Do you understand? - 'Verstehst du?'
EDIT: Sie essen das Salz.
The subject and object of the sentence doesn't really matter. "Die Kuh hört den Hund" or "Die Frau hört den Mann" or "Die Kinder hören die Mutter" it's all the same. What's important is that you learn how to use it and you can use it for anything after that. You don't learn the sentence here, you learn the basic idea.
Die Eule teaches basic German grammar rules and a relatively small German vocabulary. It is up to the learner to add to their vocabulary and create their own sentences.
It also helps to read and learn the details of the basic grammar rules, as well as additional, more advanced usage.
Jedoch, ist mir egal was eine Küh Herde."
Hmmmm . . . doesn't seem to work as well auf Deutsch, Abbott. We'll have to do something different when we play Munich.