In "The Lottery," how does the drawing, determining who gets stoned, work?

There are actually two drawings in the lottery. The first drawing is only for heads of households. The black box contains only as many slips as there are households in the little community. All of the slips except one are blank. One slip is marked with a big black dot. On the day of the lottery described in the story, the black spot is drawn by Bill Hutchinson. That means that someone from his family of five will be selected to be stoned.

Mr. Graves had selected the five slips and put them in the box. and he dropped all the papers but those onto the ground. where the breeze caught them and lifted them off.

Mr. Graves, who assists Mr. Summers, collects all the slips of paper used in the first drawing for heads of households. There are five people in the Hutchinson household: Bill, Tessie, and their three children, Bill Jr., Nancy, and little Davy. So Mr. Graves keeps four blank slips and the slip with the black spot drawn by Bill Hutchinson and puts these five in the box. All the other blank slips are allowed to be blown away by the breeze. This will prevent any member of the Hutchinson family from picking up a discarded blank slip and keeping it to pretend he or she had drawn it if that person happens to draw the slip with the fatal black spot. Tessie Hutchinson might be capable of doing something like that.
The household has been determined by the first drawing. Now the five members of the Hutchinson family are the only ones to participate in the second drawing. One by one they draw their slips--but they do not open them until the whole family has drawn. Then Mr. Graves opens little Davy's slip for him. The crowd utters a sign of relief because they would prefer not to stone a two-year-old child to death.

Nancy and Bill. Jr. opened theirs at the same time. and both beamed and laughed. turning around to the crowd and holding their slips of paper above their heads.  

The other two Hutchinson children are delighted to be spared this year, even though it means that either their mother or their father will be sacrificed and they will have to participate in the stoning.

"Tessie," Mr. Summers said. There was a pause, and then Mr. Summers looked at Bill Hutchinson, and Bill unfolded his paper and showed it. It was blank.

Tessie has thus far declined to open her slip. She seems to have had a premonition that she is fated to be the "winner" of this year's lottery. When her husband opens his slip and shows it is blank, that makes it obvious that Tessie has the black spot. But she still clutches it tightly in her hand unopened. 

Bill Hutchinson went over to his wife and forced the slip of paper out of her hand. It had a black spot on it, the black spot Mr. Summers had made the night before with the heavy pencil in the coal company office. Bill Hutchinson held it up, and there was a stir in the crowd.

The horror of being stoned to death by three hundred friends and neighbors has even turned the Hutchinsons against each other. Tessie is all alone in the world. She continues protesting, "It isn't fair, it isn't right!" as the others close in for the kill.