Is there a rule why “Kočka žrádlo žere.” is not correct here? In other cases I saw the SOV word order as well.
"Kočka žere žrádlo." is a simple statement.
"Kočka žrádlo žere." is not usual word order. You may say "Kočka to žrádlo žere!", if you were surprised the cat is eating some particular type of food, for example.
“Kočka žrádlo žere.” is correct. It just wasn't added yet.
"Kocour jí žrádlo", proč ne?
"jí" = "eat" used for people, while "žere" is used for animals
But it is not strict, especially not for pets.
Here it is rejected because of the kocour = tomcat.