Quote analysis essay of how to kill a mockingbird

The excerpt is from a longer essay on huckleberry finn by mark twain. what kind of support is used to develop the writer's main idea regarding how twain brought his characters to life?

The greatest gift the sumerians gave the world was the invention of writing. the sumerians were a wealthy people. they needed some way to keep track of what they owned. they began drawing pictures. they used a reed as a pen. they drew on soft pieces of clay. the soft clay was then dried in the sun. the tablet became a permanent record. later, the sumerian drawings changed into wedge-shaped symbols. this kind of writing is called cuneiform. by putting symbols together, the sumerians could write entire sentences.

What is the phrase a tiny shoot of phase prikled by the mind