猫をかぶる (Neko wo kaburu)

Literally: To wear a cat on your head

Example: “彼女は先生の前では猫をかぶっている。” — In front of the teacher, she acts as if butter wouldn't melt in her mouth.

English equivalent: Butter wouldn't melt in someone's mouth

Origin: Two theories compete, and neither has fully displaced the other. One reads the phrase quite literally, pointing to real cat behavior: cats can act innocently docile around people while remaining capable of considerably wilder, more unpredictable behavior when nobody is watching, making the animal a natural symbol for concealing one's true nature behind an agreeable surface. A second, wordplay-based theory reaches instead for "nekoda," an old woven straw mat, proposing that "wearing the nekoda" — covering yourself while pretending not to know something you actually do — gradually shifted, through a shared sound, into "wearing the neko" (cat), with the animal only entering the picture as the mat's name was reinterpreted over time.