But one is not enough. 但这远远不够

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
155. and the rewards for the effort can be disappointing.
     努力捕食却往往空手而归
156. To say the least.
     这么说毫不夸张

来自《行星地球 第二季 第二集 Planet Earth S02E02 山脉》第 153 行