[For Seniors] Challenge Your Brain with Super-Hard Quizzes! A Collection of Tough Questions That Feels Great Once You Know the Answer

Yayoi period

The origin of onigiri is very old. Excavations and other archaeological research have revealed that as early as the Yayoi period, rice was already being molded into shapes similar to today’s rice balls. At a Yayoi-period site in Ishikawa Prefecture, Japan, charred lumps of rice have been discovered, and these are considered the oldest onigiri in Japan. It is thought that the practice of shaping rice by hand arose at the time for ease of preservation and portability. Therefore, the beginnings of onigiri are said to date back to the Yayoi period.

pour hot water

When you pour hot water over real salmon roe (ikura), the surface turns white from the heat, a membrane forms, and the color deepens. In contrast, artificial ikura shows little visible change when hot water is applied, but oil and coloring start to separate and float out. This difference makes it easy to distinguish real from artificial. This method is especially useful for people, such as the elderly, who may find it hard to tell them apart by appearance alone.

kept constant at all times

The salinity of seawater is maintained at an average of about 3.5% worldwide. This is because the global water cycle and the circulation of salts work over long periods to even things out. Although it can temporarily change due to factors like precipitation and river inflow, it remains nearly constant over large areas. As a result, there is rarely a drastic difference in saltiness when you swim in the sea.

Togo Heihachiro

Admiral Heihachiro Togo, a naval officer of the Meiji era, played a major role in the creation of nikujaga. While studying in the United Kingdom, he couldn’t forget the taste of the beef stew he ate there, and after returning to Japan he instructed a chef to recreate it. However, due to ingredient limitations, it was adapted into a Japanese-style simmered dish using beef, potatoes, onions, and the like, and this is said to be how nikujaga was born. As this anecdote spread, it came to be cited as the background for how today’s nikujaga became popular.

For fire prevention

The main reason the outlet behind a refrigerator is installed higher is to prevent fires. Refrigerators can release moisture from their internal motors, and dust tends to accumulate on the back over long periods of use. If the outlet is located low, moisture and dust can build up more easily, increasing the risk of short circuits or ignition. Installing the outlet higher reduces these risks and improves safety.

5 centimeters per second

The speed of conveyor belts at sushi restaurants is finely tuned so that customers can take plates safely and comfortably. At many locations, the standard is about 4 centimeters per second. That’s roughly just under one plate’s length per second—while it may look slow, it strikes the optimal balance that keeps both dishes and guests moving smoothly even during busy times. If it were any faster, people—including seniors—might miss plates or feel motion-sick, so careful consideration goes into setting the speed.

I was sleeping on my dominant-hand side.

During the Edo period, samurai slept with their dominant hand underneath them to protect it in case they were attacked at night. Even if ambushed and cut while sleeping, they could still fight as long as their dominant hand remained unharmed. This practice symbolizes the ever-present sense of danger in daily life and the samurai’s mindset, showing that they were expected to remain constantly vigilant.