Caution: This movie may make you afraid of your own cellphone. Kim Seong-hun's riveting if empty-headed A Hard Day will be remembered for its increasingly ominous jump-cuts to mobiles ringing, vibrating, and flashing profane messages. When the jittery camera isn't trained on these devices, it's on the apoplectic faces of their threatened owners — excepting one character who is telephoned postmortem. (In the film's most inventive sequence, this corpse is accidentally entombed with cellphone intact; it emits a loud, saccharine ringtone just as a morgue attendant is about to catch the burier.)
Aside from a jarring climax involving a precariously positioned pistol, no other gimmick is quite as intoxicating. In a very frenetic two hours, Kim demonstrates every conceivable way in which one grown man can injure another. Faces get bitten, smashed into toilet fixtures, walloped with mop handles; necks get strangled; in a blatant steal from Blood Simple, an assailant's hand is lodged in a barricaded door and tied to an attached coatrack. Flights of fancy run rampant; this is probably the only film in which an interrogator survives a simultaneous bombing and drowning. (As if these events aren't already bombastic, the score by Mok Young-jin remains at constant fever pitch.)
The plot -- a detective covers up a hit-and-run, which may or may not have been planned -- is both needlessly overstuffed and inconsequential. But A Hard Day is propelled by Lee Sun-kyun's hyperventilating turn as this harried cop. He's so exaggeratedly wide-eyed and ashen that he shows you the clownish side of full-on anxiety attacks.