His face fell when he saw the distance he still had to go.
As she read her exam results, her face fell. 看到考试成绩，她的脸阴沉下来。
You should have seen his face fall when he realized she had won.
As soon as I walked into the room, I could see their faces fall.
Their little faces fell when I told them we couldn't go to the park.
See also: fall verb (UNHAPPY)