In the Odyssey, when Odysseus enters the Underworld, what does he sacrifice?

As Odysseus and his crew enter the Underworld, they prepare to sacrifice a number of sheep. Odysseus digs a pit while his men hold the sheep, and "round its edges poured an offering to all the dead" of honey, wine and water on which he then sprinkles white barley. The pit will catch the blood of the sheep, and it is where the crew will place the bodies when they are finished. The entirety comprises their offering to the spirits with whom they wish to speak. Then he says, "with prayers and vows I had implored the peoples of the dead, I took the sheep and cut their throats over the pit, and forth the dark blood flowed."

Odysseus likewise prays to the dead and promises that, when he returns home to Ithaca, he will offer his best cow as well as one sheep, "wholly black, the choicest of [his] flock" for the deceased blind prophet, Tiresias, with whom he is most anxious to speak.