**Core Concept**
Cadaveric spasm, also known as instantaneous rigor or cataleptic rigidity, is a rare phenomenon where the muscles of a deceased person contract immediately after death, often preserving the last moment's pose or gesture of the individual. This condition is distinct from the more common rigor mortis, which develops several hours after death due to muscle protein degradation.

**Why the Correct Answer is Right**
Cadaveric spasm is thought to occur due to the sudden loss of neural activity and the subsequent unopposed contraction of muscles, which are triggered by the intense emotional or physical stimulus experienced by the individual at the moment of death. This phenomenon is often associated with sudden, traumatic, or violent deaths, where the body undergoes a brief, intense period of muscle contraction before the onset of rigor mortis.

**Why Each Wrong Option is Incorrect**
**Option A:** Cadaveric spasm typically occurs immediately after death, whereas rigor mortis develops several hours later. This statement is incorrect because it confuses the timing of the two conditions.
**Option B:** Cadaveric spasm is not a result of post-mortem changes, such as putrefaction or decomposition, which are unrelated to the phenomenon. This statement is incorrect because it misattributes the cause of cadaveric spasm.
**Option C:** Cadaveric spasm is not a reversible condition, as it is a fixed, irreversible contraction of muscles that occurs at the moment of death. This statement is incorrect because it implies that the condition can be reversed.

**Clinical Pearl / High-Yield Fact**
It is essential to note that cadaveric spasm is a rare and exceptional phenomenon, and its occurrence should not be taken as evidence of a specific cause of death. In forensic pathology, the presence of cadaveric spasm should be carefully documented and considered in conjunction with other evidence to establish the circumstances surrounding the individual's demise.

**Correct Answer: C. Cadaveric spasm is not a reversible condition.**