A Slovene by birth, my father-in-law isn't very familiar with American jokes. So he was a little taken aback when his Mujo and Haso joke was followed by a:
He paused, thought a little bit and then replied with a hearty grin:
The house erupted in laughter. "No, Dad, you're supposed to say "who's there?" one of his daughters said. The joke took on a life of its own because it was indicative of the difference between the Yugoslavian culture he grew up in and the American culture he was celebrating Christmas in.
From the meter man to the next door neighbor, in small-town Croatia it doesn't matter who you are - guests are always invited in for coffee. I learned this first-hand during my first year in Croatia.
Even if you don't call ahead of time, your instant host will invite you in as if they'd been expecting you for a week. Then they'll get you out of shoes and into slippers faster than you can say "but I just came over to drop this off." By the time you get out of there, you'll wonder what happened to the previous hour-and-a-half.
Since that first year, I've learned that what probably happened during your stay is that your host neglected their garden, their plan to pick mushrooms or the elderberry flowers they were soaking in order to make juice. Or perhaps they're even late for work or an appointment. It's no exaggeration to say that in small-town Croatia, guests are at the top of any hypothetical list of priorities. Nothing trumps the person at your door. Even if they're a stranger.
So next time someone begins a knock-knock joke, make sure you beat them to the punch line. Because in Eastern Europe someone at your door is no joke.