Any TV show that’s filmed live has little signs that tell the audience when to applaud. Almost all TV shows use laugh tracks so that audience members know when to laugh, and movies have soundtracks that tell the audience when they should feel happy or sad or scared.
What do books have?
Books have words. (duh) They have words that shape the mood like a soundtrack would. They have words that give the reader clues for what’s coming next (like signs). And they have words that show character reactions, reactions that tell you when you’re supposed to laugh.
That’s what a laugh track is doing, after all. It’s a recorded track of people laughing. That’s it. Other people laughing – and it works.
Have you ever been with a group of friends, and someone said something that made one of you laugh? Then, suddenly all of you are laughing and can’t stop. But when you try to explain to someone later, they don’t understand why it’s funny. And you can’t really tell them because, deep down, you were mostly laughing because someone else was laughing, and you got caught up in the moment.
It works with clapping, yelling, violence, and even yawning. Something about our psyche is tuned into other people’s responses (See crowd psychology).
So if you have a really funny moment in your book, show the reader that it’s funny through the other character’s reactions to whatever just happened. Granted, if it was really that funny, they should be reacting anyway. But the characters’ reactions help show the reader how funny it is. They make it seem funnier. Facial expressions, body language, statements, actions, etc. become the laugh track for the book. In fact, they help guide all reader reactions (scared, disgusted, annoyed, etc.).
Now, do laugh tracks always work?
No. If a laugh track plays at a sublimely unfunny moment, people won’t necessarily laugh anyway; however, it can help make a slightly humorous moment seem wittier than it was. Don’t ask me why (I wasn’t a psych major), but people definitely react more strongly when they get the impression that other people are reacting, too.
That’s why stage performers (actors/musicians/etc.) may joke about putting a “plant” in the audience. A “plant” is someone who knows when to laugh, gasp, cheer, and so on, and those reactions help influence the rest of the audience to be more involved in the show. The term comes from how historic snake oil salesmen or stage magicians would plant a cohort in the audience to pretend to be a complete stranger who is picked to help with the show.
Well, the closest thing we have to “plants” in books are the characters we create and the reactions we give them. So why not use them to our advantage?