Which of the following is a characteristic of rigor mortis?

The characteristic of rigor mortis is that it is the stiffening of muscles after death. This phenomenon occurs due to biochemical changes in the body, specifically the depletion of ATP (adenosine triphosphate) in muscle cells. Without ATP, which is necessary for muscle relaxation, the muscles become stiff and hardened, typically starting a few hours post-mortem and peaking around 12 hours after death. It is important in forensic science as it can help establish the time of death and is a key sign used in determining the post-mortem interval.

The other choices don't accurately describe rigor mortis. For example, it doesn't happen immediately after death; it develops over a period of time. Rigor mortis also affects the skeletal muscles throughout the body, not just the internal organs. Lastly, while it is related to the post-death process, it is not a sign of decomposition itself, which involves different biological processes. Understanding rigor mortis is essential for forensic investigators as it provides critical information about the time since death.