Two space aliens depart the planet Zoltar for different locations on Earth (but each earning exactly 67,345,871,243 Star Alliance miles in the process).
One lands in San Francisco. The other lands in Berlin. Both are, understandably, quite hungry, and each one goes a restaurant to consume mass quantities of local (but non-sentient) animals. Then what?
The alien in San Francisco is presented, before even having finished, with the bill. “How rude”, thinks the alien.
The alien in Berlin is not presented with a bill at all, but only asked how the meal tasted. He finally consults his Deutsch/Zoltarisches Phrasebook to enquire for the bill. “How awkward”, thinks the alien.
In both cases, the bill comes to exactly 23 Local Currency Units (LCUs). Each alien has a 20 LCU note and a 10 LCU note in his travel pack. They use their heightened awareness to study the locals engaged in the same transactions.
The alien in Berlin tells the waiter who brings him the check to “Make it 25”, gives him the notes, gets 5 LCUs back at once, and leaves. The alien in San Francisco puts both notes in the folder, waits for the staffperson to return, then gets 7 LCUs back in change ten minutes later, puts 5 LCUs in the folder, and leaves.
Both aliens report back on the strange customs of the Earthlings.