HO-LY crap. The internet is full of weird and wonderful videos of sports injuries but not many of them feature actual aliens.
We may not have any proof that whatever is crawling under this man's skin is extraterrestrial, but there's simply no other explanation.
WARNING: Graphic footage and offensive language
The calf in question belongs to a Californian man named Angel Bermudez, who pulled out his camera phone when his muscles started contracting after a workout.
"Look at this s***," Bermudez wrote. "Painful yes it was."
"Looked like a god damn alien in my damn leg was gonna bust out," he added.
It's now been viewed more than 13 million times in what is clearly the most famous case of cramp since Sri Lankan cricket captain Arjuna Ranatunga legs started buckling under his ample weight at the SCG in 1996.