What mark of punctuation might indicate that more information is to come

When mrs. jameson says "it (the desert) won't leave you cold," what does she mean?

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.

If you were making a persuasive speech about how students should take creative writing every year they are in school, which sentence would most effectively support that argument?