**Core Concept**
Pain of pericarditis is typically sharp and stabbing, often radiating to the back, and is associated with inflammation of the pericardium. This pain is often exacerbated by lying down and relieved by sitting up or leaning forward.

**Why the Correct Answer is Right**
The pain of pericarditis is thought to be due to the inflammation of the pericardium, which irritates the surrounding nerves. When a patient lies down, the pericardial sac can become more tense, increasing the irritation of these nerves and worsening the pain. In contrast, sitting up or leaning forward can help to decrease the tension in the pericardial sac, thereby reducing the pain.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because pain of pericarditis typically worsens with lying down, not leaning forward. Although leaning forward may provide some relief, this is not the characteristic feature of pericardial pain.
**Option B:** Incorrect because pain of pericarditis typically worsens with lying down, not the supine position. The supine position can actually exacerbate the pain.
**Option C:** Incorrect because pain of pericarditis typically worsens with lying down, not during inspiration. The pain may be exacerbated by deep breathing, but this is not a characteristic feature of pericardial pain.
**Option D:** Incorrect because pain of pericarditis is not typically associated with eating. The pain may be exacerbated by lying down or other factors, but eating is not a characteristic trigger.

**Clinical Pearl / High-Yield Fact**
A classic exam question about pericarditis is to ask about the location of the pain and how it changes with position. Remember that pericardial pain is typically sharp and stabbing, radiating to the back, and worsens with lying down.

**Correct Answer: a) Pain increase on leaning forward**