“There are many, many things that are difficult in this life, but one thing that isn't difficult at all is figuring out whether someone is excited or not when they open a present. If someone is excited, they will often put exclamation points at the end of their sentences to indicate their excited tone of voice. If they say "Oh!" for instance, the exclamation point would indicate that the person is saying "Oh!" in an excited way, rather than simply saying "Oh," with a comma after it, which would indicate that the present is somewhat disappointing. "Oh," Violet said, as she opened her present. "Oh," Klaus said, as he opened his. "Oh," Sunny said, as she tore open her shopping bag with her teeth.”
Book:The Ersatz Elevator