All the time these two factors affect each other, that is why smiling when sad makes you happier and it is why you laugh when you find something funny.

这两项因素一直都是互相影响的，这就是为什么难受的时候微笑会使你开心些，同样也说明了为什么当发现有趣的事情时你会大笑。

youdao

Each time the TV cameras swoop over the smiling crowds in the Olympic venues, we are reminded that we can match anyone when it comes to putting on a show.

BBC: Brand GB �C a good games