A bender wasn't used to having their weapon completely taken from their control. Korra gave a brief shout in surprise before recovering as best she could. The transition of the kunai wasn't exactly smooth; she bent the air around the small knife to slow it down and snatch it out of the air.

Korra didn't use the kunai to block the sword, though. She fell back, dropping to support her weight on her hands as the sword whipped over her. She intended to spring back up with both feet for a kick. It should have been a firebending move, but... no fire here.