一いっ瞬しゅんにして

expression, adverb

in an instant; instantly; in a flash

Emphasizes that something happens or changes extremely quickly, often with dramatic effect. Used in both spoken and written Japanese.

• 一いっ瞬しゅんにして景色けしきが変かわった。

  The scenery changed in an instant.

• 彼かれの表ひょう情じょうは一いっ瞬しゅんにして曇くもった。

  His expression clouded over in a flash.