Before Cinderella's mother dies, she tells her daughter to plant a tree on her grave and to just shake the tree when she needs help in the future.
Cinderella is sad and abused, but at least her bird friends help her clean and complete the other menial tasks her wicked stepmother and stepsisters force upon her.
The pigeons and the tree provide the clothes and carriage needed for Cinderella to attend the royal ball, and when she leaves behind a golden slipper, the prince sets on a quest to find the foot that fits it.
To fit in the slipper, one stepsister cuts off her heel, but the birds point out the blood in the shoe and the prince knows she is not the one. The second stepsister cuts off her toes to fit in the shoe, but the birds tattle again about the blood pooling in the shoe.
In the 1857 version, the Grimms added a fun little coda, too: just before Cinderella's wedding to the prince, the birds pluck out one eye from each sister (so they can still watch their humiliation, I suppose), and then just after the wedding, the birds finish the job and peck out each sister's remaining eye. And "thus," the story concludes, "for their wickedness and falsehood, they were punished with blindness as long as they lived."
Don't go under the knife just to impress some guy.
Grimms' Fairy Tales (Illustrated Junior Library)