An example of Al-Biruni's analysis is his summary of why many Hindus hate Muslims. Biruni notes in the beginning of his book how the Muslims had a hard time learning about Hindu knowledge and culture.^[72] He explains that Hinduism and Islam are totally different from each other. Moreover, Hindus in 11th century India had suffered waves of destructive attacks on many of its cities, and Islamic armies had taken numerous Hindu slaves to Persia, which—claimed Al-Biruni—contributed to Hindus becoming suspicious of all foreigners, not just Muslims. Hindus considered Muslims violent and impure, and did not want to share anything with them. Over time, Al-Biruni won the welcome of Hindu scholars. Al-Biruni collected books and studied with these Hindu scholars to become fluent in Sanskrit, discover and translate into Arabic the mathematics, science, medicine, astronomy and other fields of arts as practiced in 11th-century India. He was inspired by the arguments offered by Indian scholars who believed earth must be globular in shape, which is the only way to fully explain the difference in daylight hours by latitude, seasons and earth's relative positions with moon and stars. At the same time, Al-Biruni was also critical of Indian scribes who he believed carelessly corrupted Indian documents while making copies of older documents.^[73] He also criticized the Hindus on what he saw them do and not do, like their deficiencies in curiosity about history and religion.^[72]