Theyyam, as it is popularly known, is a ritual form of worship of North Malabar in Kerala. This performance art is thousands of years old. The performers of Theyyam belong to the lower caste of the Hindu community, and play an important position in Theyyam. 

All the prominent characteristics of primitive, tribal, religious worship had widened the stream of Theyyam cult, where even Muslims are associated with the cult in its functional aspect and made it a deep-rooted folk religion. 

In several cult-centres, blood offering is seen, despite being forbidden in sattvic Hinduism, Jainism and Buddhism. In such centres, separate places outside the precincts of the shrine are selected for blood offering and for the preparation of the traditional Kalam known as Vatakkanvathil. The Theyyam deities propitiated through cock-sacrifice will not enter such shrines. 

Read more: http://en.wikipedia.org/wiki/Theyyam