"{one's} jaw [drop] (open|)" 的定义和意义

What is the origin of the idiom "one's jaw drops" and when to use it?

The idiom "one's jaw drops" originates from the physical reaction of a person's jaw literally dropping when they are astonished or surprised. This expression is used to describe a state of shock, disbelief, or amazement. This expression is commonly used in everyday conversation to emphasize the magnitude of one's surprise.