grin

n. 露齿笑,裂口笑
v. 露齿而笑

I knew she was joking because she had a big grin on her face.

我知道她是在开玩笑，因为她脸上堆满笑容。

They grinned with pleasure when I gave them the sweets.

当我给他们糖果时，他们高兴地咧开嘴笑了。