"There Will Come Soft Rains" by Ray Bradbury is a story about a house in the aftermath of a nuclear bomb or disaster of some kind. I will spare you all of the technical details about an atomic explosion. Here is the simplified version. It releases a ridiculous amount of energy. A portion of that energy is light and heat. A lot of light and heat. So much in fact, that it is capable of vaporizing a human body. That's what happened in the story. The blast wave incinerated the people and left scorch marks on the building. Because the humans were blocking the building wall with their bodies, the building did not get scorched in those locations. So what is left on the wall is a ghostly silhouette of the humans that blocked that part of the building from being scorched.