Fi started to learn how to laugh as early as when she was one month old. My husband was the first one to notice it. I couldn't believe it at first, but was in so much surprise when I heard it myself. Her first laughs sounded like she's clearing up her throat. We knew it's a laugh because it's her way of reacting when we're playing with her.
Fi is 3 months old now and her laughs are getting more recognizable compared to her first ones. Besides, it also comes with a big smile on her face and exposure of her cute dimples. Her laughs are sweet melody to my ears. It's a sound that I can listen to, over and over again.