
Flat as a Board
This everybody knows. What you may not know is that there are two different terms for this in Japanese, depending on the sort of board.
In Japanese, osoroshii ko 恐ろしい子 means "what a terrifying child," or "what a terrifying girl," "what a terrifying guy," "what a terrifying person," and so on.
In manga and anime, osoroshii ko refers to a pose of shock, with eyes drawn completely white, and usually with one's index finger placed across the chin, sometimes drawn in monochrome like manga, accompanied by background effects like lightning or flash lines, used when a character has realized the terrifying capability of somebody.
It originates in the drama shoujo manga, Glass Mask, Garasu no Kamen ガラスの仮面. Today, it's pretty much always used in comedy, often sarcastically. It's become a meme.
In anime, sometimes characters' "eyes become 3's," me ga san ni naru 目が3になる. As in, they become drawn as the number 3, the Arabic numeral.
This article is about "3-shaped eyes." Not to be confused with having three eyes instead of two, or having a 3-shaped cat mouth (・ω・).
In Japanese, magan 魔眼, "magic eye," or "demon eye," also called "evil eye," jagan 邪眼, or satirically jakigan 邪気眼, is an eye that has some sort of magical power or ability. Sometimes a cursed, evil, demonic one.