啃骨头 kěn gǔtou
(1) [gnaw a bone;pick a bone]∶用牙剥食骨头上的肉
那只狗在啃骨头
(2) [a job that was difficult and not very profitable]∶比喻难做的而又没有什么油水的工作,常和“吃肉”对举
吃肉和啃骨头的事都得干