**Core Concept**
In medical negligence cases, the burden of proof typically lies on the plaintiff (patient) to establish a prima facie case. However, there are exceptions to this principle, which shift the burden to the defendant (doctor or healthcare provider).

**Why the Correct Answer is Right**
One such exception is the doctrine of res ipsa loquitur. This Latin phrase translates to "the thing speaks for itself," implying that certain injuries or events are so unlikely to occur without negligence that the mere fact of their occurrence is evidence of negligence. In cases where the patient can show that the injury or event would not have occurred without the doctor's negligence, the burden of proof shifts to the doctor to provide an explanation for the incident.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a clear exception to the burden of proof. Without more context, it is difficult to determine if this option is relevant to the question.

**Option B:** This option is incorrect because it is not a recognized exception to the burden of proof in medical negligence cases.

**Option C:** This option is incorrect because it does not accurately describe an exception to the burden of proof.

**Clinical Pearl / High-Yield Fact**
Res ipsa loquitur is a doctrine that can be a powerful tool for patients in medical negligence cases, as it shifts the burden of proof to the doctor to explain the cause of an injury or event. This doctrine is often applied in cases where the patient can demonstrate that the injury or event would not have occurred without the doctor's negligence.

**Correct Answer: C. Res ipsa loquitur.**