and other entheogens. Prāyaścitta - an expiation ritual performed if a puja has been performed wrongly Nyasa, installing mantras on the body Ritual purification (of idols, of one's body, etc.) Yatra: pilgrimage, processions Vrata and Samaya: vows or pledges, sometimes to do ascetic practices like fasting The acquisition and use of siddhis or supernormal powers. Associated with vamachara ('left-hand path') Ganachakra: A ritual feast during which a sacramental meal is offered Ritual music and dance Sexual yoga: ritual sexual union (with an actual physical consort or an imagined deity) Dream yoga. Worship and ritual Worship or puja in Hindu Tantra differs from Vedic forms somewhat. While in the Vedic practice of yajna there are no idols, shrines, and symbolic art, in tantra they are important means of worship. Rituals are particularly important in the dualistic Śaiva Siddhānta which according to Padoux "is typically characterized by an overabundance of rituals, which are necessarily accompanied by mantras. These rituals are not so much a succession of actions as a play of mentally visualized and experienced images, a situation common to all Tantric traditions, where rites, meditation, and yoga are exercises in creative identifying imagination." The theory behind these rituals is the idea that all humans have a fundamental impurity (mala) that binds them to rebirth. This impurity can be removed by ritual action (along with proper knowledge). The initial step in this path is the ritual of initiation (diksa), which opens to door to future liberation at death. In the non-dualistic and transgressive (or "left hand") traditions like the Kali cults and the Trika school, rituals and pujas can include certain left hand path elements that are not found in the more orthodox traditions. These transgressive elements include the use of skulls and other human bone implements (as part of the Kapalika vow), fierce deities like Bhairava, Kubjika and Kali which were used as part of meditative visualizations, ritual possession by the deities (avesa), sexual rites and offering the deity (as well as consuming) certain impure substances like meat, alcohol and sexual fluids. Padoux explains the transgressive practices as follows:On the ritual and mental plane, transgression was an essential trait by which the nondualistic Tantric traditions set themselves apart from other traditions – so much so that they used the term "nondualistic practice" (advaitacara) to refer to the Kaula transgressive practices as a rejection of the duality (dvaita) of pure and impure