Which of the following is a key symptom indicating neuromuscular involvement?

The key symptom indicating neuromuscular involvement is an eye muscle disorder. Neuromuscular involvement can manifest through various symptoms that affect muscle control and coordination. When there is a disorder specifically affecting the eye muscles, it may indicate issues with the nervous system's ability to control these muscles, which are integral to activities such as focusing and eye movement. Conditions like strabismus or diplopia, which involve eye muscle dysfunction, are directly linked to neuromuscular issues.

The other choices do not specifically signal neuromuscular problems. For example, failure to complete projects may be related to psychological or motivational factors rather than muscle control or neurological function. Constant motion could point toward hyperactivity or restlessness, but it is not a definitive indicator of neuromuscular involvement. Unpredictable behavior generally pertains to emotional or psychological instability rather than a clear indication of neuromuscular issues. Therefore, the presence of an eye muscle disorder serves as a clear and specific symptom that suggests neuromuscular problems.