The circumstances of any natural disaster will always vary, but in the aftermath there are, without failure, a few reliable outcomes. Our leaders will inform us everything possible is being done, and that help is arriving presently; people far and wide will send their thoughts and prayers to the victims; and a shark will swim down the highway.

Last night, for example, a shark was spotted swimming along I-75, just outside of Naples, Florida, in the flooding following Hurricane Irma. The shark, it probably does not need to be said—or should not, anyway—was not really there. In fact, the man who posted it admitted as much when called out on it. “Actually, it’s been going around for 12 years,” he said of the image. Despite that, the tweet has picked up steam gradually today, to the tune of more than 1,500 retweets.

It’s hard to say how many, but a certain number of people sharing the shark today are likely in on the joke, coming as it did just two weeks after the most successful example of the Highway Shark meme following the floods in Houston, which was shared almost 90,000 times. But very many of them are sharing it in earnest, just as it was shared during Hurricane Joaquin in South Carolina in 2015, Sandy in New Jersey in 2012, back to its emergence in Hurricane Irene in Puerto Rico in 2011, and in nearly every other natural disaster in between.

As many have since pointed out, to no avail, the image seems to have been copied from a photograph of a shark following a kayaker in 2005 published in Africa Geographic.

And so, there is no shark. And yet the shark is all there is.

The reason why one might share it is obvious: Going viral, baby! The impulse for that, of course, comes with its own set of related psychoses. Jason Michael, the Scottish man who shared it, told Buzzfeed that poking fun at people’s susceptibility to it was the plan all along. “Of course I knew it was fake, it was part of the reason I shared the bloomin’ thing,” he said.

But the reasons why others continue to fall for it every time are a bit more complicated. Partly it’s that we’ve become a nation of eternally gullible rubes damned to kick at Lucy’s infernal football of idiocy as penance for our media illiteracy, but also because the shark is a metaphor for our collective hysteria.

For all of the good social media has done at connecting us—and in times of disaster it’s been an invaluable tool in many constructive ways—there is often a perverse tendency to feel left out when you’re on the outside looking in. Social media serves as a sort of instrument of Stolen Disaster Valor. If we can’t be flooded out of our own homes, we can feel like we’re there ourselves. Perhaps not on the ground, but at least manning the switchboard. But times of stress can wreak havoc on our skepticism.

After a while, the thrill of disaster rounds off to a dull banality. Streets turned into canals are exciting at first, but a spectacle isn’t a spectacle forever. So, we revert to the pleasure-giving centers of our brains and engage in flights of fancy in order to keep the high going, like studio execs giving notes on a script. What this scene of carnage and pain needs is a pack of lions escaped from the zoo, or a damn-ass shark, because what is more titillating to humans than the apex predator unleashed from its confines of the sea, now on the hunt in our very streets? I’m getting juiced up just thinking about it right now.

Nevermind that it’s not real, nevermind that it’s not likely. From the Salem witch trials and the monkey-man of Dehli to the menacing clown sightings of last year, our susceptibility to the collective illusion of threats, real or imaginary, is well-documented. Highway Shark is the mascot for and manifestation of our self-created fear. And like many sharks, it has to keep moving forward to stay alive.

In recognizing that, you have a choice: You either become the person who posted the shark, or you’re the person who shared it. Predator or prey.