1. The lion picked off the weakest member of the herd.2. We singled him out as our opponent because he is the weakest of his team.
pick offpick off 就是挑一個人或動物下手, 已經有攻擊的意思. single out 只是指挑一個人或動物
My sister is bad-tempered and would sna at anybody whenever she feels like it.