Don't sleep with yout mouth open.

Don't sleep with yout mouth open.
Don't sleep with yout mouth open.

Don't sleep with yout mouth open.
open是来修饰mouth的
表示张着嘴
希望能帮到你（有什么问题可以直接hi）

睡觉别张着嘴 open形容词表示状态，作后置定语修饰mouth,

Don't sleep with youR mouth open.
睡觉时不要张开嘴

不要张着嘴睡觉

with** 介词+宾语 ，open作为补语放在名词之后