**Core Concept**
Bell's palsy is a unilateral lower motor neuron lesion of the facial nerve (cranial nerve VII) causing facial paralysis. Hyperacusis, or an increased sensitivity to sound, is a common symptom in these patients.

**Why the Correct Answer is Right**
The stapedius muscle is responsible for stabilizing the stapes bone in the middle ear and reducing sound intensity. Paralysis of the facial nerve leads to the paralysis of the stapedius muscle, resulting in an inability to dampen sound, causing hyperacusis. This is due to the loss of efferent innervation to the stapedius muscle, which normally helps to modulate sound through the process of acoustic reflex.

**Why Each Wrong Option is Incorrect**
**Option A:** The orbicularis oculi muscle is responsible for eye closure and is not directly involved in sound modulation.
**Option B:** The digastric muscle is involved in jaw movement and is not related to sound sensitivity.
**Option C:** The tensor tympani muscle is another muscle involved in sound modulation, but it is innervated by the mandibular division of the trigeminal nerve (cranial nerve V), not the facial nerve.

**Clinical Pearl / High-Yield Fact**
The stapedius muscle's role in sound modulation is an important aspect of otolaryngology and can be relevant in the diagnosis and management of patients with hearing or balance disorders.

**Correct Answer:** C. The stapedius muscle.