baby got back

why is it that babies (even those that are still inside mummy's gooey uterus), including mine, love the song baby got back?  Last night Ryan spent an hour or more singing to my belly and our little blob started kicking.  Until he sang I like big butts and I cannot lie, big butts and I cannot lie.  He seriously went wild inside and was kicking like there's no tomorrow. haha.  it is funny.  Next time I need to take a video of my belly while he is dancing to baby got back because you can see the belly waving and moving haha.  So cute!