After following Sarah's story for close to two years, we are just beginning to find out, reports CBS News The Early Show national correspondent Tracy Smith.
The daughter of a proud Midwestern family, her life at 18 was filled with goose bumps and laughter and promise. But one night in 1984, just after midnight, a drunk driver hit Sarah and threw her into the path of a second car which struck her directly in the head.
Her brain was injured so severely Sarah should have died over 2 decades ago, but did not.
"They never tell you what the prognosis is for a head injury," said Sarah's mother, Betsy Scantlin.
"The brain injury is so severe that the daughter you had is gone," said James Scantlin, Sarah's dad. "It's been destroyed."
Sarah lay motionless for several weeks. When her eyes opened she did not seem awake, her expression blank. Not awake, not asleep. Days led to weeks and to months and the years slowly rolled on.
Then 20 years later, in early 2005 …
"Suddenly the phone rings one day," James Scantlin recalls. "Oh boy, that was something."
"She said 'It's Sarah,' and I said 'It's Sarah?'" Sarah's brother Jim Scantlin said. "And she said 'Hello!,' and I just went numb."
After 2 decades at life's edge, Sarah was talking.
No one knows for sure, but looking back, there were clues along the way.
"As I'm walking around the room she would still keep her eyes on me, watching what I was doing," said Jennifer Trammell, Sarah's nurse for 20 years.
At year 14, Sarah began to scream, especially when people left her.
"She yelled at me the whole way out," said Jim Scantlin. "So I could hear her all the way out the door."
Sarah would yell out for six more years.
"It took her that long to try to get out even one word," Trammell said.
"I did feel that there was some increased activity going on within her mind," noted Dr. Brad Scheel, Sarah's doctor.