@Katzenjammer, I have to think it's a combination of signaling, timing and specific available nutrients (mammals and mollusks only) and biomass. It's even wei

@Katzenjammer, I have to think it's a combination of signaling, timing and specific available nutrients (mammals and mollusks only) and biomass. It's even weirder, because the lungs cough up, eat, swallow, poop the eggs. Snails eat rat poop, and then hatch the eggs and poop larva in their slime. Rats eat the snails and the larva infest and follow the nerves up the spine. Once sexual maturity is reach they go to the lungs to spawn and die. The distance is too far in humans, so they actually only have enough time as sexually mature adults to cross the distance of a rat's body. When they die inside a human, they've spent too much time and traveled the distance of longer than more than one rat's body.