The movie anaconda is a boat swallowing, man hunting monster. The real green anaconda, Eunectes murinus, is something stranger: a study in biological efficiency. This episode starts with the name. The Carib people called it the great snake, while Carl Linnaeus in 1758 gave it a Latin label that actually means mouse hunter. It then takes on size. Guinness notes that no living animal has been more exaggerated, and 19th century naturalists repeated rumors of 30 and 40 foot specimens. Dr. Jesus Rivas has measured more than 900 wild anacondas, and the longest was a female just over 17 feet and about 214 pounds.

What the snake does with that bulk is the remarkable part. It floats with only its eyes and nostrils above the surface, drowns prey as large as capybaras and caimans, and walks its jaws over the carcass on stretchy ligaments while breathing through an extendable windpipe. Females dwarf males, sometimes eat them, give birth to live young, and can reproduce with no male at all. The episode closes in Florida, where that same adaptability has made the species a prohibited invader.

• On a 1937 expedition in Guyana, team members guessed a resting anaconda at 20 to 60 feet. The tape measure said 19 feet 4 inches.
• Tanned skins can stretch by more than 50%, which is why museum hides once passed as proof of 30 foot giants.
• Up to a dozen males wrap around one female in a breeding ball that can last two to four weeks, using pelvic spurs that are remnants of hind legs.
• In 2014 a female housed alone at West Midlands Safari Park in the UK gave birth to three healthy young through parthenogenesis.
• As of August 2023 at least 11 green anacondas had been verified in the wild in Florida, from Gainesville to Homestead. The state added the species to its prohibited list in April 2021.