A video of a venomous snake is drawing interest online for one — well, two — clear reasons: When the snake opens its mouth in a yawn-like motion, a pair of very large fangs briefly swing into view like folding blades.
The video, posted on social media by Mark's Reptiles (@marks_reptiles), showcases a Gaboon viper named Francisco. The species bears the longest fangs of any venomous snake on Earth.
The video's caption suggests that Francisco was stretching by unhinging his jaws, exposing his fangs, and folding them back up after a large meal.
While it may appear like he is yawning, the mouth-opening motion is not a sign of drowsiness after eating. It is part of the way the viper repositions its jaws after swallowing prey, so its mouth is properly aligned for future feeding or defense, according to A-Z Animals.
Gaboon vipers are the largest vipers in Africa, according to the Smithsonian's National Zoo & Conservation Biology Institute, with some exceeding 45 pounds and over 6 feet in length. They are also ambush hunters, and because they are not built for speed, they depend on precise strikes and highly specialized anatomy.
Their fangs can reach roughly 2 inches in length and are hollow and curved backward, a structure that helps deliver venom deep into prey. Their camouflage is also integral to their hunting, as they can easily blend into a leaf-littered forest floor in preparation for a surprise attack.
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After feeding, the snake may open its mouth wide to help realign its flexible jaws. Gaboon vipers, like many snakes, swallow prey whole, which can cause the jaws to come out of alignment after opening incredibly wide.
When the snake is not striking, its fangs lie folded against the roof of the mouth. During an attack, they rotate outward to an angle of about 180 degrees. In Mark's video of Francisco, the yawning motion briefly reveals that hidden mechanism, showing how much of the snake's weaponry stays out of sight when the mouth is closed.
On his YouTube channel, Mark says that the goal of his content is to educate people about snakes and dispel fears, which are often rooted in online misinformation.
While the species is capable of delivering a large venom yield in one bite — around 7 to 9 milliliters of wet venom, or as much as 1,000 milligrams in dried form — Gaboon vipers are not especially known for biting people, according to A-Z Animals. They are generally calm animals and only attack humans if provoked.
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Still, their venom is both cytotoxic and hemotoxic, meaning it can damage or kill living cells and cause internal bleeding.
Francisco's mealtime ritual is a useful reminder to treat wild animals with caution and to respect their space.
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