One thing's for sure: Eventually, something's gonna tickle that little funny bone. Douglas's oldest daughter first laughed when Douglas emerged from the shower with a towel wrapped around her head. "It was like, 'Silly Mommy, that's not what you use towels for!'" she says. (Laughing at a "crazy" scene shows healthy cognitive development, too, because it means your child has ideas about the way things ought to be.)
Other things that trip the funny-o-meter for the diapers-and-burp-cloth set: games like peekaboo that provide anticipation and a pleasant surprise; a bit of gentle physical play, like tossing her a few inches in the air (for older babies); and, lastly, good ol' slapstick.
Your child's laugh may be high-pitched and choppy, as if he's channeling Flipper the Dolphin, due to his baby-soft, floppy larynx. Grab a video camera and enjoy: By around a year of age, his larynx will tone up, and he'll simply sound like a little kid with a big sense of humor.
source : http://www.parenting.com/article/Baby/Development/Baby-Laughter