You practiced laughing all day. Staccato giggles and coughing guffaws, accompanied by equal parts naivete and skepticism. It didn't matter whether something was funny, or ironic, or so tragic that you had to laugh or you'd cry. You were simply engaging a new vocal movement. Not testing its practical applications so much as kicking its tires, putting it through the paces. This laugh will come in handy some day, you're quite sure of it. Just not sure when.
Sure, it happens naturally when your mom makes the crocheted giraffe stampede all the way from your feet up to your face. It also happens naturally when your dad takes a warm washcloth and scrubs your neck, armpits, hands, and feet. But there are more uses, you're quite certain. Just need the practice for now.