Forrest Gump is full of American historical and cultural allusions. The part about shit "shit" is like this: The man was trying to seek some inspiration from Forrest Gump when he suddenly saw Forrest Gump stepping on it. Shit, he couldn't help shouting "shit!" which means shit. Unexpectedly, A-Gump said "it happens" without any care, which means "sometimes it does happen." The man was greatly inspired by this and invented the phrase "shit happens" "It means "bad luck happens from time to time". Later this sentence became popular in the United States, and many cars posted this slogan, similar to the "Please keep distance" posted on cars in our country. Then the next shot is posted with The car with this slogan collided with another car, which really fulfilled the saying "shit happens".

As for the smiling face, there is /view/1192114.html in Baidu Encyclopedia