They all were protective over an object. James was protective of his glasses, Remus was protective of his chocolate, Sirius was protective of his hair, Peter was protective of his food and Lily was protective over a necklace given to her by Petunia. No matter what Petunia called her, Lily loved her to much to take of that necklace. Only Petunia and Lily know the meaning of the necklace and over the holidays Petunia would subtly and secretly check for the necklace.