Ɔirno fell from a tree. さるの木から落ちる (Saruno ki kara ochiru) Original proverb: 猿も木から落ちる (Saru mo ki kara ochiru) "Even monkeys fall from trees." Loose translations: "Anyone can make a mistake." "Even Homer sometimes nods." "さるの" (Saruno) is a misspelling of "ちるの" (Chiruno/Cirno), the first character "ち" (chi) is mistakenly flipped into "さ" (sa). "Saru" means "monkey" in Japanese.

* Correction: Ɔirno -> Cirno Saruno -> Cirno

That means she accidentally fell from a tree when she was sleeping on it, but maybe she is all right because she is the strongest.