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

boiled egg

Terms like “rare” and “well-done” are now used mainly for the doneness of meats such as steak, but they originally came from French and were used to describe how boiled eggs (egg dishes) were cooked. “Rare” referred to soft-boiled, while “well-done” meant hard-boiled. Over time, the usage spread to meat dishes, and today these terms are chiefly associated with doneness in cooking meat, though many people may be surprised to learn their origins.

Because I'm eating the concrete block wall.

A snail’s shell is made mainly of calcium, and they need a lot of it for growth and protection. Concrete and stone block walls often contain calcium on their surfaces, which snails consume and absorb to reinforce and repair their shells. That’s why they often gather on block walls. Although predator avoidance and food availability also play roles, calcium intake is considered the main reason.

triple

Camels have triple-layered eyelids. In addition to the usual upper and lower eyelids, they possess a third eyelid (the nictitating membrane) that moves horizontally. This membrane is semi-transparent and protects the eyes while maintaining vision even during sandstorms. As a result, camels can live in harsh environments like deserts without injuring their eyes. This triple eyelid is a unique feature of camels that is not seen in many other animals.

doctor

The “Monster Teahouse” that appeared in Omori, Tokyo, in 1830 is said to have been founded by a physician named Hyōsen. He excelled not only in medicine but also in devising entertainment and eccentric projects. At the time, haunted houses were not yet a common form of amusement, but Dr. Hyōsen created one through various ingenious ideas to surprise and delight people. This concept became the root of today’s haunted houses, and he is remembered in history as someone who combined medical knowledge with a playful spirit.

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.