This article is a bit misleading.
See, on the surface, it says that laughing burns more calories than your basal, or "resting" metabolic rate.
That sounds really exciting. Laugh yourself skinny, right?
Only see--what they compared it to was sitting watching TV.
Your body never burns fewer calories than when you're sitting watching TV. You could sit and talk and burn more calories than sitting watching TV, since you'd be moving your mouth, gesturing, etc. You could hiccup and burn more calories than sitting watching TV.
So as far as exercise goes, they admit right in the article this is a great way to burn about four and a half pounds a year.
So don't swap your Kathy Smith videos for Marx Brothers just yet. Or, if you've already memorized the Smith routines, then maybe you can go ahead and make the swap and watch Groucho and Harpo while you do the memorized routines. Now that's multitasking.