Mudrās play a very significant role in the Tāntric rituals. They are generally poses of the body or of the fingers. They are said to be endowed with mystical and magical effects.
One of the 25 mudrās mentioned in the Gheraṇḍa Saṁhitā (3.77 & 78) and other such works, is the aśvinī-mudrā. It consists in contracting the anus and the genital organ and dilating them again. It is said to increase the strength of the body and build up its resistance to diseases.
See also MUDRĀS.