Final answer:
Eurycleia recognizes Odysseus by a scar on his leg, which serves as a significant plot device in the narrative for character revelation.
Step-by-step explanation:
Eurycleia, the old nurse of Odysseus, recognizes him based on a distinguishing scar on his leg. This discovery occurs when Eurycleia is washing Odysseus' feet, and upon seeing the scar, memories from the past are stirred, allowing her to identify her master who has been away for many years. Literary techniques such as physical marks like scars often play crucial roles in ancient epics for character recognition; they serve as effective narrative tools to advance the plot and highlight significant revelations.