BAY CITY, Tex. — “I’m gonna mash ‘em out.” Ryan Ashcraft spotted some cattle loitering in standing water under a clump of trees and came out of a long, sweeping curve in his small helicopter to drop toward a clearing so narrow it seemed the blades might give the treetops a haircut — and potentially send Mr. Ashcraft and his passenger on a one-way trip to the afterlife. Mr. Ashcraft, 22, dipped toward the cattle and then pulled up sharply and hovered; the maneuver made the blades produce a sharp POP-POP-POP-POP-POP. The animals hate the noise, which puts many of...