Definition: Given a scientific passage and an answer, generate a question for the given answer.
Input: Passage: The digestive system of birds is unique, with a gizzard that contains swallowed stones for grinding food. Birds do not have teeth. What do you think the stones do? They help them digest their food. Defining characteristics of modern birds also include:. Answer: swallowed stones
Output:
What does the gizzard in birds contain that allows them to grind food?