A horseshoe crab is fucking gnarly, bro. You see this brown, almost crescent/spherical object with a pointy tail skuttling along innocuously at the bottom of the shallows, and moving at a decent pace. It's so different from anything else you'd expect to see with the tides, and much larger too. Bigger than any crab, bigger than most fish that like to hang at that shallow depth. You might even mistake the two round black dimples in it's carapace for eyes, and like the comical depiction find it...cute?

It looks fairly non threatening, and has a poor reaction time. So like any kid you pick it up by it's tail, and then, "HOLY FUCK!" Nightmare fuel, as you look under it's carapace at the many legs writhing underneath like some Cthulhu fever dream.

You put it back down in the water and continue to let it do it's thing.

I've had that experience a couple times, but I've never witnessed these things breeding before. My Mom who was an Environmental Chemist for the EPA saw these things breeding once, and it's like a giant migration for these crabs to the shallows and shore. We're talking absolutely hundreds of them coming to fuck in some nasty orgy and peace back out to sea.

Certainly one of the weirdest, coolest and oldest creatures on Earth.