Kumbhaka is the central practice of traditional Hatha pranayama; there are two types of retention: after an inhale (antara), and after an exhale (bahya)
Nowadays we simply shoo pigeons away from our public gathering places. But in Vedic times, 3,000 years ago, the pigeon was a bird of ill omen, the messenger of the goddess Nirriti, a personification of misfortune, misery, and death.