The ram and black ewe were to be killed at the ritual trench.
See evidence text
“‘‘When you shall have thus besought the ghosts with your prayers, offer them a ram and a black ewe, bending their heads towards Erebus; but yourself turn away from them as though you would make towards the river. On this, many dead men’s ghosts will come to you, and you must tell your men to skin the two sheep that you have just killed, and offer them as a burnt sacrifice with prayers to Hades and to Proserpine. Then draw your sword and sit there, so as to prevent any other poor ghost from coming near the spilt blood before Teiresias shall have answered your questions. The seer will presently come to you, and will tell you about your voyage—what stages you are to make, and how you are to sail the sea so as to reach your home.’ ”