To be frank its Jiang Shi not chiang shih …
Moving corpse are divided into 2 types of categories
1) Jiang Shi which is normally buried for a long time or which is dead due to loss of blood.
2)Xing Shi which is dead but able to walk like normal people but is kinda slow.
Jiang Shi meaning for stiff corpse are stiff of course, its believe that if it consume blood, and the blood will continue to pump through the body , and the Jiang Shi would be able to move a little bit better not as stiff as before for a short period.
The time is directly affected to the amount of blood consume.When the blood drys up, the corpse will starts to get stiff.After long period without having blood,it will starts to dry up and would start to rot causing it to be unable to move again unless blood is drip in to the body causing it to get away from stiffness.