With his sharingan still active, sasuke watched as korra began to wave her sword irregularly, and soon he realised there was multiple waving hands that looked like willow tree being blown by the wind, but something was off, the hands were not really attached to anything or anyone, nor do they try to attack him, now recognising it was a genjutsu, sasuke first assessed his chakra flow by looking again at his hands, before breaking the genjutsu with his sharingan, sasuke then draws his kusanagi with his right hand, holding the blade in reverse form, he blocks the incoming sword attack
Sasuke just broke the previous illusion, and then realised that bean vines grew from the earth beneath him and constraint him, and korra emerges from a bean pod, it was then sasuke realised that he doesn't really feel the texture of of the bean vines binding him, nor do he smell the vines, he quickly realised to was a genjutsu, and so he pierced through the visual illusion using his sharingan