The four of us occupied the whole cabin in the train when we were still in Austria. A cabin had six seats; three seats in a row facing opposite the other three seats. All the seats could slide down so that we could lay down to sleep. Not too comfortable, but cheaper than buying a ticket with sleeper.
We read that night trains are dangerous and there are thieves that might spray sleeping gas in night trains. Thus, we were extra careful with our belongings; we slept on our bags. Our friend even chained our cabin door so that we could all have a peace of mind that no one would come in and took our things when we were asleep!
Around midnight, there were suddenly a lot of passengers boarding the night train. We thought they were Italians. Then came a loud knock. It was an Italian police officer. He wanted to check our passports as we were entering Italy. My friend quickly unchained the door for him.