Roughly once every eight to nineteen years, determined by a specific and irregular rule of the lunisolar calendar involving an extra month falling in the lunar month of Ashadha, the wooden images of Jagannath, Balabhadra and Subhadra are entirely replaced in a ceremony called Nabakalebara, new body, in which specific trees meeting exacting traditional criteria are located, felled and carved into new images before the old ones are ceremonially retired.
The most closely guarded part of the ceremony is the transfer of the brahma padartha, a sacred substance believed to constitute the living essence of the deities, from the interior of the old wooden images into the newly carved ones, a rite performed at night by specially designated priests, blindfolded and with their hands wrapped in cloth so that they cannot see or directly touch what is transferred, and the details of what is actually moved have never been disclosed outside this closed priestly process, making Nabakalebara one of the clearest instances in Hindu temple practice of a central ritual whose specific content is deliberately kept unknown even to most of the tradition's own devotees, let alone to outside observers.
Pulling the ropes of the chariots is traditionally open to anyone present regardless of caste or religion, a rare instance of a core ritual act at a major Hindu festival carrying no restriction on who may perform it, consistent with the theological point that the festival exists precisely to bring Jagannath out to people who could not otherwise approach him inside the temple, including those historically barred from entering it.