What in the world is THAT sound?!

Okay, so I hear Mommy's heartbeat everyday, all day long- but why am I hearing a second heartbeat? Mommy told me a very nice lady from her work let her borrow a prenatal education system. It's called Baby Plus (www.babyplus.com). She says it's an "auditory exercise" what will strengthen my learning ability. I am not sure about it but I make sure to kick and move around whenever she turns it on. Mommy says it feels like I am dancing to the beat!!! I've got rythm! Each week I learn a different heartbeat which gets faster each week. I am learning how it sounds different from Mommy's heartbeat and of course my very loud canine sister and brother, Leena and Fenton.