In chapter 4 of To Kill a Mockingbird, Jem and Scout are thrilled that summer has come again. Summer means no more school and best of all, it means Dill will be back. When Dill arrives, the three of them begin their tradition of trying to get Boo to come out of his house.
Dill wants to know what a "hot steam" is and Jem is more than happy to tell him.
"A hot steam's somebody who can't get to heaven, just wallows around on lonesome roads an' if you walk through him, when you die you'll be one too, an' you'll go around at night suckin' people's breath."
Dill is not convinced that this is true, but part of him does believe it. There are many superstitions in the south and this is just one of them. Jem and Scout grew up hearing these things and they want Dill to be as educated about them as they are. Jem, Scout and Dill are obsessed with all things creepy. They love they creepy story of Boo, and that is one of the reasons they want to try to get him to come out of his house so badly. The three of them have no idea that the real creepy things are just about to begin and they are more than superstitions.