What does Mattie see on the steps of a house that deeply disturbs her?

From the text:

“What’s that?” I asked, pointing to something on the marble steps of a three-story house.
“Don’t look, Matilda,” said Grandfather. “Turn your head and say a prayer.”
I looked. It appeared to be a bundle of bed linens that had been cast out of an upper window, but then I saw a leg and an arm.
“It’s a man. Stop the wagon, we must help him!”
“He is past helping, Miss,” the driver said as he urged on the horses. “I checked him on the way out to fetch you this morning. He were too far gone to go to the hospital. His family tossed him out so as they wouldn’t catch the fever. The death cart will get him soon for burying.”