**Core Concept**
Pocks on chick embryo are a classic example of cytopathic effect seen in viral infections. These lesions are formed due to the replication of viruses that cause cell death, resulting in characteristic pock-like depressions on the surface of the embryo.

**Why the Correct Answer is Right**
The formation of pocks on chick embryo is primarily due to the cytopathic effect of the virus, which leads to cell lysis and death. This is a result of the virus's ability to hijack the host cell's machinery and replicate itself, ultimately causing the cell to burst and die. The pocks are formed due to the accumulation of dead cells and the subsequent collapse of the tissue.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not directly relate to the formation of pocks on chick embryo.
**Option B:** This option is incorrect as it refers to a different type of viral infection that does not cause pocks on chick embryo.
**Option C:** This option is incorrect as it is a different type of viral infection that causes a different type of cytopathic effect.

**Clinical Pearl / High-Yield Fact**
The chick embryo is a widely used model in virology to study the cytopathic effects of viruses. The formation of pocks on chick embryo is a classic example of the cytopathic effect and is used as a diagnostic tool to identify viral infections.

**Correct Answer: A. Varicella Zoster virus causes rash, not pocks on chick embryo.**