very interesting. Your post has prompted my to actually test if any body parts catch fire, and i have ended up with some weird results. It seems nothing actually catches fire while immersed in magma. i have set the damage, liquid and boiling point of default bone template to 1000 (extremely low). Normal creature upon creation immediately catches fire( if just placed on solid ground) and completely burns out within 2 sec. Skeleton dropped in water (if dropped on solid gound just burns forever) catches on fire and burns for about 5 sec, and then his bones liquify (legs, head, lower body etc etc. ) but still stays alive somehow and shows all body parts missing, but is still mobile and can walk around, even ettack other creatures. Its like he has some invisible spirit holding his being together. Similar results are observed with zombies. If left on solid ground eventullay burn to their bare bones. However(!) if dropped in water, their bones quickly liquify and the zombie is left with rotting outer shell ( skin, sinew, muscle) without any bones inside them ( they evaporated). Still fully functional and mobile. If killed (either zombie or skeleton) on open air, their remains quickly evaporate. As i said these tests are done with modified raws with bones evaporating on open air, but it shows that undead are somehow exempted from tissue damage that normally damages other creatures.