once they have a hold, they never let go. 一旦被它逮住 猎物再无逃脱的机会

112. From memory, the wildebeest are coming
     鳄鱼凭着记忆得知 角马已经来了
113. and gather in anticipation.
     不出所料 它们纷纷下水
114. The crocodile's jaws snap tight like a steel trap -
     鳄鱼的巨口像捕兽铗一般紧咬住猎物
115. once they have a hold, they never let go.
     一旦被它逮住 猎物再无逃脱的机会
116. It took over an hour to drown this full-grown bull.
     它得花上一个多小时 才能淹死这只成年公角马
117. To surprise their prey
     为了突袭猎物
118. crocodiles must strike with lightning speed.
     鳄鱼必须以闪电般的速度出击

来自《行星地球 第一季 第三集 Planet Earth S01E03 淡水》第 115 行