I'd say that's roughly correct. Czech and Slovak have a different sound, melody. Czechs and Slovaks tend to underestimate the differences, because they largely

I'd say that's roughly correct. Czech and Slovak have a different sound, melody. Czechs and Slovaks tend to underestimate the differences, because they largely understand each other. But that's to a large degree thanks to a large amount of interchange and exposure. These days, many young Czechs without exposure to Slovak often understand only very little Slovak.