A Visit From a Previous Owner

"Mommy! Mommy! Look what I found!" Jimmy ran into the kitchen, where his mother was washing dishes, as quickly as his four year old legs could move.
"What is it, sweetie?"
"Pretty white rocks!" he handed them over.
"These are pretty! Let's clean them up, okay?"
Jimmy jumped with excitement, "Hurry! I wanna dig more!"
"Jimmy, these- these are teeth! Where did you find them?!" she gasped, dropping the molars into the sink.
"In the back yard, why?"
"Whose body is buried in my yard?" she asked herself.
"My invisible friend, George, told me to dig there, and there's more!"