Firecrackers go off, and I hop behind what suddenly looks like a pretty flimsy metal railing, on a bridge over the scenic River Duero, as a more than 1,200-pound bull bolts past, chased by villagers.
This spectacle, the Toro de la Vega festival in Tordesillas, a two-hour drive north of Madrid, has been repeated almost every year, on the second Tuesday of September, since medieval times.
Locals chase the bull into a field on the edge of town, where others, on horseback, wield spears.
For centuries, the bull would then have been stabbed to death, slowly. But this year, that final bloody act was banned.
Back in May, the regional government of Castilla y León outlawed it, after years of protests and lobbying by Spanish animal rights groups.
Many locals are furious.
"Tordesillas will not surrender!" they chant, decrying the animal rights movement, political correctness and the media. Some wave spears and vow to kill the bull anyway, risking arrest.
"This isn't about defending the life of one brave bull. It's about defending rural traditions," says Laura Giménez, 57. "If you want to talk about abuse, look at all the refugees, look at all the children starving in the world! People are worried about one bull here?"
Giménez fears this type of ban could spread to other rural festivals, and chip away at rural life in Spain.
"It's the central part of our festival. It's our happiness. If you take that away, what do we have left?" she asks. Most of her relatives have already moved to larger cities, in search of work.
The new ban on killing bulls applies only to this one festival, which has been renamed Toro de la Peña, though most Spaniards still use the old name.
Bullfighting, in which bulls are also stabbed repeatedly and then killed, is still legal in all but two Spanish regions, and widely practiced, though attendance has dwindled since the economic crisis.
The words of the Tordesillas town anthem are all about killing "brave bulls." Its annual festival is one of the most gory and famous — and thus became a focus for animal rights activists in recent years.
"In Spain, there are two countries living in the same moment. It's like I live in the 21st century, and you still live in the 15th century!" says Silvia Barquero, president of PACMA, an animal rights political party founded in 2003. "People still believe they can kill bulls only for fun, and the rest of people, who believe now is the time to end with all these cruel traditions."
Barquero spent 10 years lobbying for the ban on killing bulls in Tordesillas, and believes Spanish public opinion is turning against bullfighting and other traditions many consider inhumane.
This past summer, her PACMA party sent activists undercover to film another festival in Toledo, south of Madrid, where a baby bull was tortured and stabbed to death by drunken revelers. The footage went viral on social media, with 20 million views in the first 24 hours, according to PACMA.
Last week, thousands attended an anti-bullfighting protest in downtown Madrid. It was the largest such rally in years.
"Torture is not culture!" protesters chanted.
One of them, Jorge Rodriguez, is a vegetarian and gay, two things he says his grandparents had no experience with. But Spain is at a crossroads, he says. It had a nearly 40-year military dictatorship, which ended with General Francisco Franco's death in 1975, the year before Rodriguez was born. The country has since transformed itself, to become one of the first in Europe to legalize gay marriage. Animal rights are next, Rodriguez believes, but he says it takes time.
"Our traditions are linked to our history. It's a lot more than hurting animals for the sake of hurting animals," he says. "You know, this is rooted — and that's why it's so difficult to get rid of it."
Back at Tordesillas' annual bull festival, a yelling match breaks out between dozens of animal rights protesters and thousands of festival goers, both calling each other "cowards."
One protester is in tears. Mounted police encircle the animal rights activists, to protect them from the angry crowd.
But just then, the sky opens up, drowning out their rival chants, and dousing everyone with the first rain in months. Both groups run for cover, and find themselves huddling together under the same awnings. The festival comes to an early close.
The exhausted bull, meanwhile, is escorted away to a nearby corral. He'll eventually be slaughtered for food. But for now, he's the first animal in centuries to survive this spectacle.