How does nurse Eurycleia recognize Odysseus in The Odyssey?

Eurycleia has known Odysseus ever since he was a baby. Throughout Odysseus' childhood, she regularly bathed him. When Odysseus was a youngster, he sustained a scar on his leg from a wild boar during a hunt, and it's this mark by which Eurycleia recognizes her lord and master when he returns to Ithaca after his epic voyage.

Odysseus' wife, Penelope (who still thinks that Odysseus is a beggar), has instructed Eurycleia to bathe the stranger. As she does so, Eurycleia sees the scar on Odysseus's leg and immediately recognizes him. She's overjoyed to see her king once again, but Odysseus still has unfinished business, so he tells Eurycleia not to reveal his true identity, even to Penelope. First, he has to settle accounts with Penelope's suitors. Then everyone will know who he is.