**Core Concept**
Cadaveric spasm is a rare and instantaneous muscle contraction occurring at the moment of death. It is often seen in individuals who die suddenly or unexpectedly, such as in cases of homicide or accidental death. This phenomenon is distinct from rigor mortis, which develops hours after death.

**Why the Correct Answer is Right**
Cadaveric spasm typically occurs immediately after death, without any delay. This is because it is a reflexive response to the sudden loss of neural input, rather than a gradual process like rigor mortis. The affected muscles are usually those involved in the final act or struggle before death, such as in cases of hanging or drowning. **Voluntary muscles**, including those of the limbs and trunk, are commonly affected by cadaveric spasm.

**Why Each Wrong Option is Incorrect**
**Option B:** Cadaveric spasm does not occur after 2 hours of death, as it is a distinct entity from rigor mortis, which develops hours later.
**Option C:** Cadaveric spasm affects **voluntary muscles**, not involuntary muscles, which are typically involved in autonomic functions like digestion and circulation.
**Option D:** Cadaveric spasm does not affect involuntary muscles, which are not typically involved in this phenomenon.

**Clinical Pearl / High-Yield Fact**
It is essential to distinguish cadaveric spasm from rigor mortis, as the former can provide valuable information about the circumstances surrounding a death. Cadaveric spasm can be a key piece of evidence in forensic investigations, particularly in cases where the cause of death is unclear or disputed.

**✓ Correct Answer: A. ac**