When Xena and Ulysses are passing the sirens' island, Xena attempts to sing over them to keep Ulysses from jumping off the boat. Lucy Lawless did the actual singing for her part.
This show tries to give an ancient Greek slant to stuff but had to call this character by the familiar name 'Ulysses', which is the Roman name for the Greek hero 'Odysseus'.
At 10:30 for the first time we see Gabrielle as a dancing temptress, no longer the innocent young girl in the first season.
To save Ulysses, Xena sings more loudly than the sirens' song. Giving him earplugs (as in Homer's Odyssey) would have been easier but much less dramatic.