warm a snake in one’s bosom字面意思在胸口暧热一条蛇，真实含义是姑息坏人；施恩于忘恩负义之人；养虎为患。

【例句】
Never warm a snake in your bosom.
永远不要施恩于忘恩负义之人。

The boy whom they were fostering attacked their son with a knife. They were warming a snake in their bosom.
他们收养的那个男孩拿小刀袭击了他们的儿子。他们是在养虎遗患。