This is Lesson I of the BabyPlus curriculum. The sound is familiar, repetitive and not complex compared to the sounds the prenatal child hears every minute of every day, but the child detects the difference. The child begins to compare and contrast, that is, to employ the most basic learning principle at this critical time of development.
The pattern has increased significantly in speed, and the pattern is more complex and the subtle variations in tone are again audible to the child. BabyPlus may sound repetitive and basic to the adult ear, but to the prenatal child it is a logical and instructive progression. By this time the child will often begin to move around when the lesson begins. This is a great time for bonding.