In Chapter 4 of "To Kill a Mockingbird," in what way does Jem unintentionally get even with Scout?

ON page 43-44 of chapter 4 Dill has just arrived from Mississippi and the children are trying to decide what to play.  Dill says that he "smells death" and the kids start talking about "hot steam."  Jem explains the theory of how to avoid death by the "hot steam" while walking down a road at night, but Scout contradicts him and tells Dill not to believe him.  The children decide to play roll the tire and Jem lets Scout go first.  Ms. Lee writes from this point from Scout's point of view:

"Until it happened I did not realize that Jem was offended by my contradicting him on Hot Steams, and that he was patiently awaiting an opportunity to reward me.  He did, by pushing the tire down the sidewalk with all the force in his body.  Ground, sky and houses melted into a mad palette, my ears throbbed, I was suffocation.  I could not put out my hands to stop, they were wedged between my chest and knees.  I could only hope that Jem would outrun the tire and me, or that I would be stopped by a bump in the sidewalk.  I heard him behind me, chasing and shouting."