Listening to this now, and very much enjoying the conversation!
Here are a few points that come to mind;
Regarding the image of seminal fluid "spreading through the limbs", I think Lucretius may be making an inference by analogy. He seems to think of this fluid as being associated with adolescent growth and sexual maturity, which of course it is–the "springtime" of life, when the streams run high with the freshets of meltwater, and the sap in the trees runs up into the limbs and oozes out the trunk. This is actually offered as one of the definitions for the word 'sap'; vigor or energy: e.g "the hot, heady days of youth when the sap was rising".
Regarding the image of "falling toward the wound", he seems to be drawing on the ancient association between Mars and Venus, war and love–the arrows of Cupid. The way that intense love, particularly when unrequited, can feel like a kind of trauma. When Romeo overhears his friends mocking him because of his obsession with Rosaline, he says (to himself and the audience) "They jest at scars who never felt a wound." But he felt the wound, deeply–and yet rather than recoil from this trauma, he found himself drawn ever closer. The connection between the young man's "spurt of fluid" and the dying soldier's gush of blood is then too easy to pass up–and certainly any ancient reader of Homer would have been accustomed to imagining such violent scenes.
QuoteNow the son of Tydeus was in pursuit of the Cyprian goddess [Aphrodite], spear in hand, for he knew her to be feeble and not one of those goddesses that can lord it among men in battle like Athena or Enyo the waster of cities, and when at last after a long chase he caught her up, he flew at her and thrust his spear into the flesh of her delicate hand. The point tore through the ambrosial robe which the Graces had woven for her, and pierced the skin between her wrist and the palm of her hand, so that the immortal blood, or ichor, that flows in the veins of the blessed gods, came pouring from the wound...Diomedes shouted out as he left her, "Daughter of Zeus, leave war and battle alone, can you not be contented with beguiling silly women? If you meddle with fighting you will get what will make you shudder at the very name of war."
Iliad, translated by Samuel Butler
The poet W. B. Yeats was a great lover of Lucretius, and his commentary on this passage about love is often found separated from its Lucretian context; "The tragedy of sexual intercourse is the perpetual virginity of the soul." Our bodies touch, but we can never be close enough to satisfy the desire that love instills.
I haven't finished listening, but I am certainly enjoying it