If you're squeamish, now would be a good time to look away.
Last week, an Australian man named Andre B. posted a YouTube video taken from a Snapchat sent by a friend.
The video showed a man's calf muscle visibly cramping, and it is horrifying. Unsurprisingly, it quickly went viral on Reddit.
His calf first tenses up, then the muscle appears to ripple before relaxing. The freakish saga lasts a mere 10 seconds, but it's enough to stick in your mind forever.
The man, who remains anonymous, had apparently just finished exercising: He completed 45 minutes of intense interval training, alternating two minutes of sprints with 60-second rest periods.
He reportedly explained,
I was resting at home straight after exercise when suddenly my calf locked up two times, then I managed to record the last one only. This hasn't happened to me before. It was random and it didn't hurt at all — just a weird feeling.
It may not have hurt him, but it's certainly painful to watch.
Check out the creepy clip up top.