“If you whistle at night, snakes will come out!” (夜、口笛を吹くと蛇が来る) is one of Japan’s more curious superstitions. Despite its strange wording, the belief is commonly explained in two ways.

One explanation is supernatural: whistling after dark is thought to attract monsters, evil spirits, or yokai (妖怪). The other interpretation is more historical and symbolic. In this case, the “snakes” are said to represent dangerous or shady people. In old Japan, criminals such as thieves or swindlers were believed to use whistling to signal one another while moving about at night.

Whether imagined as spirits or as real-world wrongdoers, both explanations reflect the same idea. Careless whistling after dark could invite something best left undisturbed.

This superstition comes from the Japanese word for thumb, oya yubi (親指), which literally means “parent finger.” Spot a hearse, and you are supposed to quickly hide your thumbs in your palms to protect your parents from an early death!

If that was not unsettling enough, there is an even creepier version. It claims that spirits clinging to the hearse can sneak into your body through the gaps around your thumbnails. Keeping your thumbs hidden is said to block their way in.

This one ranks high on the creepy scale. The superstition says that if you cut your nails at night (夜に爪を切る), you will not live long enough to see your parents’ death. In other words, you will die first!

The fear partly comes from wordplay. “Cutting nails at night” (夜爪) sounds exactly like a phrase meaning “a shortened life” (世詰め), both read as yozume. There is also a practical reason behind the warning. Long ago, people used knives to trim their nails, and doing that in the dark was a terrible idea.

“If you lie down right after eating, you will turn into a cow!” (食べてすぐ寝ると牛になる) is obviously not meant to be taken seriously. Still, it is a phrase many Japanese kids hear growing up.

It is mainly a playful way for adults to scold children after meals. The idea is simple: do not be lazy, sit up straight, and behave yourself after eating.

“Let spiders live in the morning, kill spiders at night” (朝の蜘蛛は殺すな、夜の蜘蛛は殺せ) is a classic Japanese superstition stating that seeing a spider in the morning brings good luck while such an occurrence brings bad luck at night. One theory is that the spider’s morning visit symbolizes a guest during the day, while the nightly encounter symbolizes a thief.

Hearing a crow’s cawing can mean multiple bad things, for someone dying right now to illness and accidents, and even a large earthquake occurring soon. This superstition is closely connected to Japanese mythology, in which a large crow called Yatagarasu (八咫烏) acts as a divine messenger and symbolizes the deities’ will to intervene in human affairs.

One of the most widespread superstitions is to not sleep with your pillow facing north. This belief has its roots in Buddhist funeral practices, in which the deceased are laid down with their head facing north. Doing so in your sleep is said to shorten your life.

“Hide your belly button during a thunderstorm!” (雷が鳴ったらへそを隠せ) is a phrase that many Japanese people might remember hearing as children. This superstition has to do with the Japanese deity of thunder, Raijin. He is the one causing the thunder in a storm and is said to have a particular passion for children’s bellybuttons – if one is exposed, he might swoop down and devour the tasty little treat.

Much like it is supposed to bring bad luck when you break a mirror in Western cultures, Japan has a similar superstition but swaps the mirror for a comb and its teeth. This belief comes from myths about the deity Izanagi no Mikoto, who used his comb to uncover a rather nasty deception and to help him escape from pursuers, throwing it to the ground where it grew into bamboo shoots. So don’t ruin your comb, it could be a life-saver.

Much like with the hearse, people say that you shouldn’t leave your wet clothes to hang out to dry overnight is because of the lingering spirits of the dead. It is believed that those spirits cling to the deceased’s possessions – and in a time of kimono being passed down through generations, no one wants a surprise visit by great-grandmother’s ghost.