Why Can't a Clear-eyed Person Cut the Red Thread? (MK30c)

KOAN: Songyuan Chongyue’s Three Turning Words:

a. Why can’t the person of great strength lift up her leg?

b. Say something without moving your lips or tongue.

c. Why can’t a clear-eyed person cut the red thread?

—PZI Miscellaneous Koans, Case 30