"I imagine the major internal organs are the first to go - the Lyrium takes them over, bolstering the metabolism of the host and making their body more resilient to the changes that are about to occur. The circulatory and lymphatic systems are assimilated very quickly because they’re used extensively by the Red Lyrium as transport systems. The brain, too, eventually succumbs at some point, perhaps later depending on the willpower of the host, maybe in a fashion similar to how Ophiocordyceps unilateralis is able to take over the minds of ants and pilot them to propagate itself. The Red Lyrium then proceeds to cannibalize other parts of the body, replacing some of the skeleton to make room for the expanding crystals and substituting its own firm composition to maintain structural integrity and function. It uses the life essence of these cannibalized body parts to continue nourishing its growing crystals. Eventually, a threshold is reached wherein there is no spare tissue left to convert - and that’s when the Red Lyrium cannibalizes the parts of the body it was piggybacking on and crystallizes, becoming immobile and statue-like."