My newborn baby laughs in her sleep?

my daughter is 4 weeks old and she has a laugh that makes me wake up laughing at night... out of nowhere I will hear a goat like sound and look over at her and she has a huge smile on her face and she will be shaking her body in a laughing motion. it doesnt sound like a laugh at all but its hilarious cuz i know she is laughing. maybe thats how newborns laugh?? anyone elses baby do this? i didnt even know a newborn could laugh.... i wish i could catch it on video sometime. p.s. i dont mean a sound like *baahh bahh* not that kind of goat sound. its more like how a nerd with laugh.just like a hu hu hu hu hu...lol