Snakes could sprout legs and roam the Earth at any moment.
That's according to scientists who say the slithering creatures are still equipped with the gene they once used to grow limbs and that a mutation is the only thing stopping it from being activated again.
More than 150 million years ago during the Upper Cretaceous period, scientists say snakes had visible legs, but later evolved into the gliding reptiles we recognise today.
Ancient fossils show they had a complete set of forelimbs and hindlimbs - just like dogs or cats.
Boffins say the 'Sonic Hedgehog' (SHH) gene needed to grow limbs still exists in snakes, but that a mutation in the "enhancer" which controls its activation prevents it from flicking to the "on position".
“In lizards, Sonic Hedgehog stays on and acts as the motor, driving limb development all the way down into the fingers and the toes,” explains University of Florida biologist Martin J. Cohn, reports National Geographic.
The existence of the gene could even explain why pythons with limb-like features have been spotted.
In a study published by Cohn and Francesca Leal in Current Biology, it says the Sonic Hedgehog gene had been switched on in some pythons which is why they had displayed the beginnings of legs.
"These transient embryonic legs give us a window in the evolutionary history of snakes by showing us that they have retained a remarkable amount of machinery needed to make limbs," Cohn said, according to Vice.
Some Reddit users have posted findings of snakes with limbs, and although the pictures have not been verified officially, users claim they have discovered the rare reptiles.
One user claimed they found a "20cm snake... with legs". Another said they had seen a "dead snake with legs".
Researchers also revealed a whole new evolutionary cycle is no longer necessary for the phenomenon to occur, as the DNA already contains the gene required.
This also means snakes are just "waiting for the right variables" to trigger the development, according to How Stuff Works.