Yeah, Ancient Greek philosophers laid the foundation for modern thought, but they were also weird as hell when you get down to it.

Empedocles was an ancient Greek philosopher, best known for his classic idea that everyone was composed of the four primary elements, that are still used in video games and things: Earth, Fire, Water, and Air. He also thought Love and Strife were the real divine roots of reality. He was reacting against the monism of Parmenides, and perhaps the atomism of Anaxagoras and others. Those two had the much more common idea that there was either only one ultimate substance, or an infinite amount. Saying there are exactly "four" things is pretty rare.
He was also a bit of a mystic, similar to Pythagoras, his tutor. He believed in reincarnation, performed miracles, and claimed he was a god. According to one story, in order to "prove" he was a God he was going to disappear entirely after he died (kind of like Yoda does), and did this by jumping into a volcano. I guess the volcano left his iconic bronze sandals, disproving that he was a God. Not 100% clear on the logic of that one, but Ancient Greeks thought a little differently than we do today.
Find out more about him on The History of Philosophy Without Any Gaps

Ten minutes later, when Pierre shows up: "Sartre, what are you doing?"
Sartre: "You can't fool me, you aren't Pierre, you are a body-snatcher! What have you done with Pierre! I can percieve his absence in you!"
Pierre: "Okay Sartre, how much did you take?"

A big part of Sartre's phenomenology is the fact that absence itself is perceived by us.. He gives an example about going to a cafe expecting to meet his friend Pierre there. He can't find Pierre, and he noticed that "not Pierre" appears everywhere to him in the cafe, in a visceral way. The chairs, tables, and people all take on an extra property in his perception, "not Pierre". Similar there is a classic joke about Sartre: he is at a cafe (pretty much everything about Sartre always happens at cafes, he was very French), and orders a coffee without cream. The waiter apologizes and says they don't have any cream, and asks if he would like his coffee without milk instead.
Like a suspicious amount of Sartre's thought experiments, it also sounds a bit like a drug trip, possible because it was.

Socrates: "when you think about it I'm the most humble person in the world. By far, really."

To be fair if a philosopher of any kind is drowning you should probably just let them.

This is a parody of Peter Singer's Drowning Child thought experiment. He asks us to imagine someone who sees a child drowning, and doesn't help them because they can't be bothered. He claims there is no logical difference between a child drowning 10 yards away, and one starving on the other side of the world, so we are equally obligated to help both.
The argument giving by the bystanders that he is old and no longer working, and therefore a drain on society, is similar to his arguments that we should perhaps euthanize severely disabled people (via abortion), because the resources spent to care for them could be spent to help many more people, which causes more global good.

Rene Decartes watching Ghostbusters: "ahhhh, I see, the spirit world actually interacts with the physical world because of 'ectoplasm', it all makes sense now".

The term "supernatural" is kind of funny because by definition it sort of means things that don't exist. If something exists, it is part of the natural world, in that it can interact with particles via the rules of physics. If ghosts exist, for example, they can't so much disobey the laws of physics, because scientists would simply adjust the rules of physics to match what they observed in the ghosts. The most striking example of this are cryptid animals like Nessie or Bigfoot. In a way they sort of count as supernatural, merely by the fact that they don't exist. If they were ever discovered, they would be boring old natural animals. In the sea, the division is even clearer, we can imagine a cryptid enthusiast asking a scientist "do you believe in sea monsters?", and the scientist replying "oh sure, there are plenty: great white shark, orca, giant squid, etc". Here the cryptid enthusiast would become frustrated and say "no I mean like Leviathan or Kraken". The scientist might ask "isn't that just a Sperm Whale and Giant Squid?". Frustration increasing, the cryptid enthusiast says "no, I mean things that don't exist." Here our poor scientist is left to contend with the true meaning of the question: "do you believe in things that don't exist?".
There are two differences, it seems, between "sea monsters" and "sea creatures". The first is that sea monsters are named in Greek, where sea creatures are named in Latin. The second is that sea monsters don't exist.

Goddess of wisdom and military strategy? That's a nerd, come on.