Ans: a (Usually not seen before 7 months)Ref: Krishan, Vij 4th ed., Pg. 1201. Rigor does not occur in foetus of less tha seven months, but is commonly found in still bom infants at full term. Intensity of rigor depends on the decedent's muscular development. The very young, very old, and debilitated have poorly developed rigor. Children who had died after chronic illness, who had mostly confined to bed for weeks or months, also showed frequently little or no postmortem stiffness because their musculature had faded away during that time. Some expert belive that the low degree of but perceptible stiffness as absence of rigor mortis.Variables affecting onset and duration of rigor:* Variables which accelerate the onset of rigor oExogenous heat, violent exertion prior to death, seizure activity, alkaloid poisoning.* Factors which delay the onset of rigor:a. Exogenous coldb. Exsanguination haemorrhagec. Asphyxial deathsd. Poisoning by arsenicConditions simulating rigor1. Cadaveric spasm: This is a rare form of muscular stiffening which occurs at the time of death. It usually affects groups of muscles in the arms.2. Heat stiffening: This process is seen in fire deaths and involves actual cooking of the muscle fibers. Because the fibers shorten, one sees a typical "pugilistic" appearance.2. Cold stiffening: Fat and muscle become solid at temperatures less than 40deg F. Rigor will develop if a body which was frozen before rigor developed is subsequently thawed.