Meaning of the metaphor “reading with your spine”

Maybe like theres this thing people say oh I just got a chill down my spine they mean that you're reading so intense you're giving yourself chills by it.

Little Women follows the March sisters: Meg, Jo, Beth, and Amy, who live with their mother during the Civil War. After their father falls ill, Beth contracts scarlet fever, and their family suffers much financial hardship. In the end, the three surviving March sisters are able to build happy lives for themselves. Meg, Jo, Beth, and Amy March grow up in Plumfield, where their family regularly struggles to make ends meet. When their father falls ill, Jo sells her long, beautiful hair so that their mother, Marmee, can travel to be with their father. In Marmee's absence, Beth contracts scarlet fever and eventually dies. Later, Meg marries, Jo moves to New York City, and Amy leaves home to live in Paris. Laurie, a family friend who was once in love with Jo, ends up marrying Amy.          Hope this helps it wont let me put the citation link sorry