**Core Concept**
Peristalsis is a complex physiological process involving the coordinated contraction and relaxation of smooth muscle in the gastrointestinal tract to propel food through the digestive system. The initiation of peristalsis involves a multi-factorial response, including neural, hormonal, and mechanical stimuli.

**Why the Correct Answer is Right**
Local stretching of the gut wall is the primary initiating response for peristalsis. This occurs when food enters the gastrointestinal tract and stretches the intestinal wall, triggering a mechanoreceptor response. The mechanoreceptors, specifically the stretch receptors, send signals to the enteric nervous system, which then initiates the peristaltic reflex. This reflex involves the release of neurotransmitters that stimulate the smooth muscle to contract and relax in a coordinated manner.

**Why Each Wrong Option is Incorrect**
**Option A:** Hormonal responses, such as the release of gastrin and cholecystokinin, play a role in regulating peristalsis, but they are not the primary initiating response.

**Option C:** Neural responses, including the release of neurotransmitters from the enteric nervous system, are essential for coordinating peristalsis, but they are not the initial trigger.

**Option D:** Gastric acid is not directly involved in initiating peristalsis, although it may contribute to the regulation of gastric emptying.

**Clinical Pearl / High-Yield Fact**
The enteric nervous system, often referred to as the "little brain" of the gut, can function independently of the central nervous system to regulate peristalsis and other gastrointestinal functions.

**Correct Answer:**
✓ Correct Answer: B. Local stretching of gut