What's the lettuce thing about?
Alright, so. Get ready for weirdness, because Egyptian mythology has a lot of that.
One of the most prominent and foundational myths of ancient Egypt is how the god Osiris was killed and dismembered by his brother Set (in some accounts, after an affair with Set’s sister-wife, Nepthys, who then gave birth to Anubis), put back together by his sister-wife Isis, then made the god of the afterlife. When she was piecing her husband back together, she found all but one of the fourteen chunks of him that had been scattered across Egypt by an enraged Set. That chunk would be his penis. But never fear, for Isis is the goddess of fertility, so she made her husband a new one out of wood (thus explaining why embalmers would make false ones for the actual dead). So completed, she rode him and became impregnated with a son, Horus (the Falcon, not to be confused with Horus the Elder, the Hawk, who was these four’s presumably-long-suffering brother). Osiris then went off to be ruler of the dead somewhere in the vicinity of the stars we call Orion, leaving the question of who was to rule the land of the living - his elder brother and semi-justified murderer Set, or his legitimate yet posthumous son Horus?
This brings us to The Contendings of Horus and Set, which is ostensibly an epic battle of order vs chaos, but mostly involves a lot of letter-writing and whinging back and forth between the gods because some liked Horus (who was the last king’s son and generally a guy who liked order and not usually killer [except that one time when Isis got too involved and actually wounded Set herself which Horus was not about for some reason and so decapitated her] ) and some liked Set (who was powerful and experienced and had good relations with foreign powers [being that he was the god in charge of them] and had proven himself to be a great protector to Ra against Actual Evil God Apophis and his night demons and whatnot). There were a lot of pointless squabbles between the two involving weird god things like who could hippopotamus better or build ships out of stone (spoiler alert: Set actually built his ship from the top of a goddamn mountain and managed to make it float long enough to get halfway down the river, Horus just made his from pine when no one was looking and just plastered the thing to look like stone. Who was the better dude in that one? You decide.). One time Horus got his eye ripped out and Set lost his testicles - an incident which involved what is probably the oldest recorded pick-up line in history: “How lovely your backside is. How broad your thighs.“ Smooth, uncle Set. Smooth.
Anyway, after eighty years of this the supreme god version of Ra got tired of their shenanigans and told them to lay off for at least one night, for all of their sakes. Set looks at Horus and goes, “Yeah let’s do this thing. Party, my house, tonight.” Horus looks at Set and thinks, “Seems legit.”
So they go party at Set’s house. Just them and the servants and lots of honey and beer and the single bed made up all nice just for them. Halfway through the night, Set rolls over and puts his dick between Horus’ thighs. (Er, depending on the time period you’re reading the myth from, this act is either consensual or not. It mostly depends on how vilified Set is by whichever cult’s in power at the time. In any case, Horus is awake and unrestrained for this.) Horus catches the semen in his hands, and when he gets home in the morning shows his mother. Who promptly freaks out, cuts his hands off to toss into the Nile, fashions him new hands of clay, and then jacks her son off into a pot.
I could not make this up.
This is where The Lettuce Thing comes in. The lettuce species that the ancient Egyptians had was a long, hard stalk that secreted a white, milky substance when cracked and squeezed. So you can see where they would get the idea that it was a phallic aphrodisiac. Well, it so happens that when Isis went to Set’s house, she found out from his gardener that Set loved eating lettuce every day. You know where this is going. Now, I’d like to point out that she didn’t just randomly overhear this and got a wicked idea. No. No, she went and asked outright what Set’s favourite food was, because she was gonna give Set a taste of his own (or well, her son’s) medicine no matter what.
Fast forward to the next court session, and Set - being the asshole that we know and love - decides to announce to the room at large that he should get the throne, because he totally tops. Well, being that ancient Egypt was a highly patriarchal society it - like most ancient cultures - looked down on the receivers in male-male relationships. But while everyone’s boo-hissing at Horus, he just calmly requests a Magical Pregnancy Test for both his and Set’s semen. They do it, and Set’s shows up somewhere in the river (wherever Horus’ old hands are), which perplexes Set and somehow doesn’t phase anyone else. Then they test Set, and lo and behold Horus’ seed reacts from within him!
In very old versions of the myth, this is where the god Thoth is born from Set’s forehead. In others, it’s Thoth performing the test and so the semen emerges in the form of golden disc, which Thoth promptly takes and puts on his own head as a crown. *shrug* Egyptian mythology is a weird case where a jillion different cults formed, then came together, then fought/reformed/vilified/reconciled/destroyed/assimilated one another over millennia, so the origins and motives are a bit wonky. Thoth is one of those deities that had been worshiped before writing was even a thing [although writing became his Thing], and so has many conflicting origin stories - mostly he just seems to appear at some point due to the power of his own voice. I like to think that, since he is also a master of Time, that Thoth may have actually created Himself in that instance, but his presence got spread out through time - back far enough into the beginning that he could trick the moon into giving up five extra non-month days each year, so that Nut could birth his parent-grandparents without repercussion.
But I’m getting ahead (behind?) myself. The point is, now all the gods think their Powerful Guy Set is a big fat bottom, which ~a king shouldn’t be~ and Set is all butthurt about his trick backfiring on him. He sulks off to the river, where he issues the stone boat challenge mentioned earlier but then his boat sinks and he rips up part of Horus’ and realizes that it’s just disguised wood, and it looks like the shenanigans will continue until someone gets the bright idea to just fucking write to the dead king about what his wishes were (apparently it’s Thoth who suggests this, which is why I buy the myth that this is when he was born, since why did no one else - even Isis who resurrected the guy - think of that? Finally, a god of Sense!). Osiris sends them a letter back to the effect of “What the fuck do you think my wishes are. If my son isn’t instated, my next gift basket will be an army of zombies, I swear to myself.”
The council is convinced.
Set’s put in chains and brought before them by a gloating Isis, but he cedes with as much grace as he has left. In most versions of the myth, he’s set free and reinstated as Ra’s bodyguard to thunder away happily in the desert, and in a few later ones (basically after Lower Egypt takes over Upper Egypt) he’s punished somehow, like being taken to the north and bound there by his other wife (in something rather similar to Loki’s fate with Sigyn). In some, he and Horus reconcile and even bless pharaohs together, tying their lotus and reed together around the living king as a symbol of unity and strength between Upper and Lower Egypt.
And that, dear Anon-chan, is The Ancient Egyptian Lettuce Thing.