Indian Penal Code, 1860
377. Unnatural offences
Whoever voluntarily has carnal intercourse against the order of nature with any man, woman or animal, shall be punished with 152[imprisonment for life], or with imprisonment of either description for a term which may extend to ten years, and shall also be liable to fine.
Explanation- Penetration is sufficient to constitute the carnal intercourse necessary to the offence described in this section.