Even by the standards of Spanish bullfighting, it seems particularly cruel.
The tradition of 'El Toro Embolado', or 'the bull with balls' still thrives in the region of Valencia, specifically the province of Castellon, and to a lesser extent in Zaragoza and the Catalan province of Tarragona. Simply put, it involves organisers setting fire to a bull's horns and then unleashing the terrified animal to run wild.
The roots of the tradition, which is also known as 'Bou Embolat' in the Valencian dialect, are unknown, although it is thought to date back as far as the pre-Roman period. The routine has evolved little over the centuries; the bull is tied to a post, and the festival organisers attach to its horns an iron contraption holding a pair of flammable balls.
The balls are then set on fire, in the hope that the animal, once unleashed, thrashes around wildly to put out the fire, like a bucking bronco on speed.
Although devotees claim the bulls aren't actually harmed during El Toro Embolado, Spanish animal rights activists strongly disagree. They have complained bitterly about the tradition, claiming bulls regularly die during the event and can also be blinded, causing them to crash into people or objects.
In the video below, filmed in 2012, a bull is seen lying dead after crashing in panic with its horns on fire (warning: this footage may be distressing).
To make life even harder for the bull, some variants of El Toro Embolado also involve a matador, who taunts the dazed animal as it runs around in flames. This can be hugely dangerous for both bull and matador, as shown below.
Those campaigning for an end to this brutal festival received some welcome news earlier this year, when all such events were banned by Valencia's regional government.
However the ban is clearly taking time to come into force. Just a couple of weeks ago, a 15-year-old boy in Villareal was killed by a bull as it tried to extinguish its flaming horns.
Another interesting approach has been trialled by the town of Los Fayos in Zaragoza, which this year replaced the burning balls on the bull's horns with LED lights. However this only succeeded in angering both sides; the traditionalists thought a sacred custom was being violated, while the animal rights activists thought the attempt at moderation didn't go far enough.
With activists still protesting and traditionalists staunchly clinging to one of the most distinctive cultural tropes of north-east Spain, it may take years to extinguish the fires for good.