att vara rädd som en hare

Literally: To be afraid like a hare

Example: “Under åskvädret var hunden rädd som en hare.” — During the thunderstorm the dog was scared stiff.

English equivalent: To be scared stiff

Origin: Draws directly on genuine, easily observed hare behavior: hares are naturally cautious, hyper-alert animals with no real means of defending themselves against predators, relying entirely on quick reflexes and an early instinct to flee at the very first sign of danger rather than risk any kind of confrontation. That skittish, always-ready-to-bolt temperament made the hare an intuitive natural symbol for timidity and jumpiness across Scandinavian folk speech generally, and the comparison is especially well documented in Finland-Swedish proverb collections, where it appears alongside other animal-based comparisons for character traits, like dum som en gås (dumb as a goose) for foolishness.