An excerpt from TV tropes:
People are fairly familiar with the story of how Set murdered Osiris to get his throne only to be thwarted by Osiris' son Horus, but most people don't know how it was done. Set attempted to prove his worthiness before the other gods by anally raping Horus, but Horus reached between his legs and caught Set's semen, throwing it into the Nile. Horus proceeded to masturbate into a salad, which Set ate without knowing about the special sauce. When it came time for Set to prove his dominance over Horus, the gods commanded Set's semen to speak. When the voice came from the Nile, the gods then commanded Horus' semen to speak, and imagine Set's state of mind when his stomach started talking to him. That is how Horus avenged his father upon Set. The Egyptians were totally perverted. One version says that they had intercrural (thigh) sex and Set (or Seth) wanted Horus to catch the semen. He did and Horus' mom saw the mess, cut off her son's hands and threw them into the river. She then put her son's semen into Set's salad and the rest you know.
I never really understood this. It clearly feels like, that seminal fluid has some sort of a meaning/purpose behind it, that is there in many myths, what I never could grasp is the following:
Knowing that myth was shaped by the humans, thus it reflected some of their idea sets (Hubris, etc...), so:
What was their "scientific" understanding on matters regarding umm... human reproduction process and it's parts, that could have influenced their myths?