Our Baby's First Laugh

Yesterday I noticed that our almost 4 months old baby started laughing when I was playing with her.  I was doing some chores and dcided to put her down on her sister's bed to take a rest while thinking of what to do in the room.  I was blowing her armpit to sound like a fart.  At first she smiled then later she was laughing.  Today she laughed again!  It's the sound that every parent wants to hear.