You won't believe the photo.
Many things happen in sci-fi movies that should stay in sci-fi movies. Take humans growing horns, for example. No one wants that to happen in real life—but unfortunately, it does.
An unnamed woman in India went to the doctor with a 2.4 inch horn growing out of her thumb. Yep, you read that right.
The case report published in BMJ tells us that the horn started growing about five years before the 60-year-old woman went to the hospital. She did have it removed three years prior, but it grew back.
Doctors diagnosed the black, curved growth as a giant cutaneous horn—or a buildup of keratin, the same protein that forms hair, skin, and nails. They removed the horn and reported that it hadn't grown back in the one and a half years since they took it off.
It's not exactly clear why these growths develop, though they usually occur on sun-exposed areas of the skin, like the face. They're often harmless, as was the case for this woman, but they can sometimes be cancerous. The authors of the report note that when they are cancerous, they're typically painful, thicker than they are long, and red and ridged at the base.
Though cutaneous horns can look similar to an animal's horns, they're actually very different. Animal horns usually form around a bone, while cutaneous horns do not.
If you notice something growing on your skin, consult your doctor ASAP. You can likely have it removed before you wake up one morning to the horror of seeing a full-on horn on your body.