看他好像吃了一惊，她感到开心。
She had the pleasure of seeing him look surprised.
知道有人欣赏我所做的事真让人开心。
It's nice to know that somebody appreciates what I do.
孩子们追逐着彼此的影子，玩得很开心。
The children were having fun, chasing each other's shadows.
我没有察觉到你那么不开心。
I didn't realize you were so unhappy.
我没有察觉到原来他那时非常不开心。
I didn't realize but he was deeply unhappy at that time.