The day was cozy sounding, enough to make you feel like going outside to have fun, and be with the people you care about.
Some of the children in the village collected some rocks. Reading this you think, "Okay, they are going to throw them or build something with them," but they start guarding them from everyone. Especially the other kids.
A pause of suspicion, the reader doesn't know what's about to happen to Tessie. Not knowing if she's okay.
The box they use for the slips of paper, is a symbol of the tradition the try to keep alive, it is also a symbol for death.
"...the flowers were blossoming profusely and the grass was richly green." The author paints a pretty and comfortable picture of how the plants in the village were growing.
The box is a methaphor for who ever gets the slip with the dot on it, it means you are going to die no matter what happens, or who gets the dot, you must die by stones being thrown.