1. The spiral staircases of most medieval castles ascend in a clockwise direction.

This is to give the defenders of the castle an advantage. Imagine two swordsmen dueling here; the right-handed defender, attacking from above, will have a much easier time striking than the right-handed attacker, attacking from below. Most people are right-handed, after all.

2. The hidden three letters "ZQM" on the ten-yuan banknote are likely intentional on the part of Mr. Zhao Qiming, the author of this set of banknotes.

3. The Colosseum originally had a retractable roof to protect spectators from the sun, but after the ravages of time, it has become what we see today!

4. In 1960, the U.S. government spent five years and $20 million training cats to be spies.

5. Tomato sauce was originally a braising liquid made from marinating fish. It was invented by the Chinese and is probably derived from the Cantonese word "egg sauce".

6. The loneliest ATM in the world is in Antarctica, surrounded by wild animals in extremely cold weather, and it doesn't see the sun for several months every year.

7. Nearly 3% of the ice in Antarctica contains penguin urine, so try not to eat the ice on the ground when you go!

8. Movie trailers used to be shown after the movie ended. You can probably guess why they were moved to before the movie started, right? Otherwise, who would stay to watch them after the movie ended?

10. Princess Wencheng was Songtsen Gampo's concubine. Xiao Qiao was not Zhou Yu's principal wife, but only a concubine.