Final answer:
Complaining of a 'bag of worms' sensation in the left scrotum suggests Marty may have a varicocele, which is an enlargement of veins in the scrotum and commonly affects the left side.
Step-by-step explanation:
When Marty, age 26, complains of a sensation of a 'bag of worms' in his left scrotum, it raises suspicion of a particular medical condition even before a physical examination.
This description is commonly associated with varicocele, which is the enlargement of the veins within the scrotum and is often described as feeling like a bag of worms. Varicocele typically affects the left side and may cause no symptoms, but sometimes it can cause pain, swelling, or affect fertility.