What does Sal see on the roof of Mary Lou's garage? Why does she say, "It made me feel peculiar"?

When Sal is visiting Mary Lou Finney’s house, she looks out the window and sees Mrs. Finney lying on top of the garage. Mr. Finney joins her and lies next to her. He puts his arm around his wife and kisses her. As Sal watches, Mr. and Mrs. Finney kiss. It is this scene that makes Sal feel “peculiar.” It reminds her of her own parents, before their baby had been born and died. Like Mr. and Mrs. Finney, Mr. and Mrs. Hiddle had not been afraid of showing their love. When their baby died, however, Mrs. Hiddle began to pull away from the family and into sadness. They tried to comfort her, but failed. Not only had she lost the baby, but she also had a hysterectomy, which means she can never have any more children. She had wanted to "fill the house with children." Though Mr. and Mrs. Finney form a touching scene, it reminds Sal of all that she, as well as her family, has lost.