Those "words" are actually sound reflexes, Priscilla says. "Babies all around the world have the same reflexes, and they therefore make the same sounds," she says. If parents don't respond to those reflexes, Priscilla says the baby will eventually stop using them.
Priscilla recommends that parents listen for those words in a baby's pre-cry before they start crying hysterically. She says there is no one sound that's harder to hear than others because it varies by individual. She also says some babies use some words more than others.
The Dunstan Baby Language DVD is currently available. Visit DunstanBaby.com to order your copy.