When we first read that Odysseus and his crew "Bore sheep aboard" (4) their ship, it makes sense to think that they're bringing these animals so they'll have some grub for their long journey. But next thing we know, Odysseus is killing and burning "sterile bulls of the best/ For sacrifice, heaping the pyre with goods,/ A sheep to Tiresias only, black and a bell-sheep" (25-27). For those of you who aren't totally familiar with sheep farming (shame on you), a bell-sheep is basically the leader or alpha sheep in a flock. So in other words, Odysseus isn't just sacrificing a few animals. He's sacrificing all the best animals. And it's not like you can eat them after sacrificing them. They have to be burned and rendered totally useless.
But why would someone go and burn his best animals, especially when there can't be all that much food to go around? Well, people in Odysseus' time, you see, felt like they'd have terrible luck if they didn't make a sacrifice to the dead every now and then. Also, Odysseus suspects that he can get the inside scoop on what'll happen in the future if he sacrifices enough animals to summon up the spirits of the dead. The "dark blood flow[ing]" (28) in the ditch basically gives the dead the strength they need to communicate with the living.
For us modern readers, the idea of sacrifice probably doesn't make much sense. The kind of sacrifice Pound is talking about here is a sacrifice without any sense of getting something back. It's just a token of respect to the dead and to the gods, and there are no guarantees that your sacrifice will come back to you in good luck. It's just something you gotta do, or else you'll anger the wrong folks.
Line 4: The sailors "bore sheep" onto the boat, but "our bodies also." That these two things are linked in this line suggests that, on some level, the sailors are not so different than the sacrificial sheep. We come to find out in line 67 that, yeah, all the sailors will die, too—just like the sheep.
Lines 22-23: Pouring out drinks for the dead might seem odd, but it's a form of gift-making, a sign of respect. (Though, who could appreciate "water mixed with white flower"? Yuck.)
Lines 25-27: Only the best will do for this sacrifice. We're guessing that a lot could be done with these valuable animals, aside from killing and burning them. All the same, Odysseus's generosity works. The dead spirits show up (though maybe not in the way he was intending).
Lines 35-37: Time for seconds. Adding to the original sacrifice seems to finally calm the restless spirits and allows Odysseus to (eventually) get the soothsaying he's after.
Line 62: It's quid pro quo out there. Here Tiresias accepts the blood and sacrifice of Odysseus and, in exchange, Odysseus gets to hear his predictions. Sacrifice is a kind of divine exchange. To get a little, first humans must give.