Final answer:
Twitching is an early sign of local anesthetic overdose, as it indicates an excitability of the nervous system before more severe symptoms appear. The option (D) is correct.
Step-by-step explanation:
An early sign of a local anesthetic overdose can include symptoms such as twitching. This occurs due to the effect of the anesthetic on the nervous system as it can prevent the initiation and transmission of sensory impulses when applied inappropriately. While other options like drowsiness, loss of consciousness, and respiratory arrest can be signs of sedatives or general anesthetic overdose, twitching is more specific and often precedes the other more severe symptoms.
Local anesthetics act to reversibly block nerve conduction, affecting both the sensory and motor functions when in contact with nerve tissue. If an overdose occurs, the increased concentration of the drug might lead to nervous system excitability, which manifests as muscle twitching before progressing to more serious conditions if not managed promptly. Therefore, option (D) is correct.