What is the saying about grasshopper in martial arts movie?

There are several different references to grasshoppers in movies, so it depends on which one you are referring to. However, most Martial Art movies that reference a grasshopper are probably doing so in connection with the 1972 pilot episode of the TV series "Kung Fu" starring David Carradine as Kwai Chang Caine (aka: "Grasshopper")

Master Po: Close your eyes. What do you hear?

Young Caine: I hear the water; I hear the birds.

Po: Do you hear your own heartbeat?

Caine: No.

Po: Do you hear the grasshopper which is at your feet?

Caine: Old man, how is it that you hear these things?

Po: Young man, how is it that you do not?