Which characteristic does NOT define post mortem lividity?

Post mortem lividity, also known as hypostasis, is the pooling of blood in the lower parts of the body after death due to the effects of gravity on the circulation. This phenomenon begins shortly after death, typically within 20 minutes to a few hours, and can indicate both the position of the body at the time of death and help estimate the time since death.

The option stating that it is reversible when the body is moved is not characteristic of post mortem lividity. Once the lividity has set in and the blood has settled in specific areas, moving the body does not cause the lividity to completely reverse to its original state. This characteristic is crucial for forensic investigations because it can indicate whether a body has been moved after death, which is valuable information in crime scene analysis.

In contrast, lividity can indeed suggest the body’s position post-mortem and help ascertain the time of death based on how long it has been since death occurred. Blood settling does not occur instantaneously; it develops as the heart ceases to pump, further solidifying these defining characteristics.