But of the things that can go wrong when hordes of humans sprint with thundering beasts at Spain's most storied fiesta, the light brown bull did one of the most dangerous on Friday, straying from the pack, spooking and charging at anything that moved.
The rogue bull gored a young Spaniard in the neck, the first fatality in nearly 15 years at Pamplona's running of the bulls. The victim was killed almost instantly as he scurried for cover under a wooden barrier, sliding under it feet-first.
Had he dived headfirst, the experienced bull runner and son of a Pamplona native would probably still be alive.
At least nine people were injured in the fourth of eight planned runs, illustrating the festival's extraordinary drawing power and global lure: two were Americans in their 60s, one of whom suffered a blow to the chest, one a Londoner aged 20, and another a young man from Argentina.
The party went on despite the death, the 15th since record keeping began in 1924. The running of the bulls - made famous by Ernest Hemingway's novel "The Sun Also Rises" - has never been suspended just because someone has died in the mad, half mile (850-meter) dash from a holding pen to the city's bull ring.
There, the same six bulls that run in the cool of the morning over cobblestone streets face off against matadors and the prospect of almost certain death in the afternoon. Ironically, on Friday, Capuchino was scheduled to go first.
A minute of silence was to be observed in memory of the late Spaniard, identified as Daniel Jimeno Romero, 27, from Alcala de Henares, a town outside Madrid. On the social networking site Netlog, where condolences were being posted Friday, he described himself as a glassmaker who loves soccer and snowboarding.
Friday's run got ugly quickly. Capuchino was running at the head of the pack at a hill leading up from the holding pen. The bulls go very fast at that point because their front legs are shorter than their hind ones, allowing them to run better on an incline than on level ground. Herders with sticks chased them, to keep them going.
But 1,130 pound (515-kilo) Capuchino, about 200 pounds lighter than the biggest of the group, tripped over some runners and ended up lagging behind.
The bulls run with six steers meant to keep them in a tight pack, and tend to mind their own business as long as they stay together. But a bull that gets separated is more likely to get frightened and aggressive, and that is what happened Friday, leading to chaos.
"As the bull approached, it attacked runners seeking refuge at the fence," said Roberto Sanz, 43, a veteran Pamplona runner who was near Jimeno Romero when he died but did not witness it.
Amateur video footage shows Jimeno Romero, wearing white pants and a brown-and-white striped shirt, trotting backward as he faced the oncoming bull and stumbling when other runners go down. He tried to squeeze under the fence, and was halfway there, when Capuchino caught him with a single swipe of his right horn.
Jimeno Romero began bleeding profusely and was tended to quickly by medics as he lay with his eyes half open.
Later, when Capuchino reached a stretch right outside the bullring, he started charging right and left, and ran back the wrong way several times. Runners sprinted to wooden barriers along the route for safety as the bull attacked. Herders tried in vain to guide it into the ring, yanking on the animal's tail to turn it around.
This went on for a minute and a half, which is an eternity at the San Fermin festival. Fast runs - the whole sprint - can end in just over two minutes.
At one point the bull picked one man up with its horns and flipped him into the air as if he were a toy, then kept going after him as he lay curled up on the ground, covering his face. He got up and ran away, and was apparently not seriously hurt.
"It was a light bull. Its charges were not particularly strong but it moved very fast from left to right," one of the bull herders, Humberto Miguel, told The Associated Press. "Of the whole pack, it was the one that gave us the most trouble."
The bulls used in Friday's run, from a ranch called Jandilla, have a reputation for being fierce at San Fermin. They hold the record for the most gorings in a single run - eight, one day in 2004.
The last fatal goring at the running of the bulls was that of 22-year-old American Matthew Tassio in 1995. Then, the problem was not a stray bull but a fatal mistake by Tassio: after falling, rather than stay on the ground and wait for the pack to pass over, he stood up and faced the animals. A bull's horn hit him right in the chest.
In 2003, a 63-year-old Spanish man, Fermin Etxeberri, was trampled in the head by a bull and died after spending months in a coma.
Fatalities are relatively rare and when one occurs, it serves as a reminder that amid all the street parties and revelry associated with San Fermin, running with fighting bulls is a life-risking exercise.