2011-08-08
Explanation
This comic explains the real-life lifecycle of trematode parasites (flukes) that manipulate their hosts' behavior. The parasite infects a horn snail and castrates it to reproduce. It then releases cercariae that burrow into the brains of killifish, causing the fish to shimmy and flash their shiny sides upward -- behavior that makes them easy targets for predatory birds. The parasite's goal is to reach the bird's gut, from which it is excreted back into the water to infect snails again, completing its lifecycle.
The comic then draws a darkly humorous parallel to humans. Since humans sit atop the food chain, it is unclear whether we are subject to similar parasitic manipulation -- but the narrator notes he "sometimes wonders about astrophysicists." The final panel shows scientists enthusiastically sending signals into space so aliens can find us, with the implication that this seemingly irrational behavior (broadcasting our location to potentially hostile aliens) might be evidence of some unseen parasitic influence compelling us to make ourselves easy prey, just like the killifish flashing their bellies at birds.