break the neck of meaning in English

做完最难部分

With the impulse of a soul who could feel for kindred sufferers as much as for herself , tess s first thought was to put the still living birds out of their torture , and to this end with her own hands she broke the necks of as many as she could find , leaving them to lie where she had found them till the gamekeepers should come - as they probably would come - to look for them a second time
苔丝对这些和自己一样的受难者，不由得动了恻隐之心，她首先想到的是结束那些还活着的山鸡的痛苦，所以她就把那些她能找到的山鸡都一个个扭断了脖子，免得它们继续受罪她把它们都弄死了，扔在原地，等那些打猎的人再来找它们他们大概还会来的第二次来寻找那些山鸡。