he uses boulders as stepping stones. 他用岩石当落脚点

148. that covers his entire territory.
     隐藏在茫茫大雪之下
149. He hunts by listening for the faintest sound of movement.
     他通过辨认极其微弱的声音来捕捉猎物
150. And to prevent crunching footsteps from revealing his presence,
     为了避免踩雪的脚步声暴露行踪
151. he uses boulders as stepping stones.
     他用岩石当落脚点
152. A mouse.
     逮住一只老鼠
153. But one is not enough.
     但这远远不够
154. The deeper the snow, the harder it is to detect prey,
     积雪越深越难发现猎物

来自《行星地球 第二季 第二集 Planet Earth S02E02 山脉》第 151 行