Belly Button is the focus of the stomach
. It attracts attention and the eyes tend to be attracted to looking at this structure. Part of the focus is the tethering function. The navel attaches the skin to the deeper structures and attracts the view during animation.
That is one reason that a beautiful belly button or something horribly ugly can make such an impact beyond its small size.
Hope this helps,
Michael Bermant, MDLearn More About Umbilicoplasty Belly Button Surgery