**Core Concept:** Lacunar infarcts are ischemic strokes that occur in the deep white matter of the brain, typically in the perforating branches of the internal carotid artery. Symptoms include hemiparesis, hemiparesis, ataxia, and dysarthria due to the involvement of corresponding brain regions.

**Why the Correct Answer is Right:** The correct answer, **Option D**, is usually related to hemorrhagic strokes rather than ischemic ones like lacunar infarcts. Hemorrhagic strokes are characterized by bleeding into the brain, leading to symptoms like headache, focal neurological deficits, and altered mental status. The other options (A, B, C) represent common symptoms of lacunar infarcts due to the involvement of specific brain regions.

**Why Each Wrong Option is Incorrect:**

Option A (Weakness on the opposite side): This common symptom is seen in lacunar infarcts because of the involvement of contralateral motor cortex, which leads to hemiparesis (reduced muscle strength) on the opposite side of the stroke.

Option B (Aphasia): Aphasia is a language disorder and can be seen in lacunar infarcts affecting the Broca's area or Wernicke's area. Broca's area is involved in speech production, while Wernicke's area is involved in language comprehension.

Option C (Ataxia): Ataxia refers to impaired coordination and balance, which can be seen in lacunar infarcts affecting the cerebellum or its connections to the brainstem and thalamus.

Option D (Headache): Although hemorrhagic strokes can cause headache, lacunar infarcts typically do not present with headache as a primary symptom.

**Clinical Pearl:** The correct answer (D) is a clinical pearl for distinguishing between lacunar infarcts and hemorrhagic strokes, as hemorrhagic strokes tend to present with headache as a primary symptom, while lacunar infarcts usually present with focal neurological deficits due to the involvement of specific brain regions.

**Correct Answer:** **D** (Headache)