Historians have identified diverse political, economic, military, religious and social causes of the Indian Rebellion of 1857. An uprising in several sepoy companies of the Bengal army was sparked by the issue of new gunpowder cartridges for the Enfield rifle in February 1857. Loading the Enfield often required tearing open the greased cartridge with one's teeth, and many sepoys believed that the cartridges were greased with cow and pig fat. This would have insulted both Hindu and Muslim religious practices; cows were considered holy by Hindus, while pigs were considered unclean by Muslims.