In a widely-circulated quote from The Sunday Times, zoologist Rob Pilley, who worked as a producer for the series, says that the dolphins "are purposely experimenting with something we know to be intoxicating," which led to them to enter a "trance-like state."
"After chewing the puffer gently and passing it around, they began acting most peculiarly, hanging around with their noses at the surface as if fascinated by their own reflection," he said.
The assumption is that the dolphins are deliberately antagonizing the pufferfish and know just the right amount of toxin to ingest to get narcotic benefits.
It is certainly funny to think of dolphins passing around a pufferfish like a joint, but discovery blogger Christie Wilcox doubts that dolphins are getting stoned.
"Tetrodotoxin simply doesn't make sense as a drug," she writes. "Every illicit drug has one thing in common: they alter minds. It's right there in the definition of narcotic. Tetrodotoxin, however, doesn't cross the blood-brain barrier; it doesn't change perception or enhance sensation."
In very small doses, tetrodotoxin can cause numbness and a tingly feeling (which might be considered a "high"), but just a smidgen too much can lead to paralysis or even death.
According to National Geographic, tetrodotoxin is 1,200 times more poisonous than cyanide. It's more deadly than even the most hard-core recreational drugs, like meth or cocaine. One pufferfish contains enough toxin to kill 30 adult humans.
Dolphins aren't "crazy enough to take that risk," Wilcox says. This probably isn't a common event and it's more logical that the dolphins were caught "paying an uncomfortable price" for harassing a potentially lethal fish.
To make her point, here's a video from 2012 of three dolphins bouncing around a pufferfish like a toy:
Dolphin researcher Justin Gregg, on the hand,
The series primers on Thursday, and the much talked-about pufferfish scene appears in the second episode.