As Told to Christina Erb
I HEARD THE CANNON and saw a wave of people running at me, and then the tips of horns shooting up. We had only run 40 yards when the bulls caught us at a sharp turn where their speed carries them to the left side of the road. So we stayed to the right and let them pass.

This was last July. I was with my brother, Sean, who's two years older than me, in Pamplona, Spain, for the annual Fiesta de San Fermin.

In April 2006, at age 24, I was diagnosed with testicular cancer and had a racquetball-size tumor below my aorta. After four months of chemo, I went into remission, and I decided that I was going to do something exciting every year to celebrate. My maiden voyage would be Pamplona, and I asked Sean to come with me.

When we arrived, we met up with some Brits who go every year, and they showed us the course—where it's safer, where it's risky, and where the bulls normally go. We got a pretty in-depth look. So we knew to stay right at that intersection.

But one of the bulls fell in the corner, and when he jumped up, he came straight at us. He got us both at the same time. His right horn went into Sean's left butt cheek and gored him eight inches deep. His left one caught me in the back of my right leg and flipped me upside down, ripping a ten-inch gash around to my knee.

In the confusion, my brother and I were sent to separate hospitals to get stitched up. When we finally got a hold of each other the next day, there was a photograph of us getting gored side by side on the front of the newspaper. We couldn't talk, we were laughing so hard.

We wanted to get the horns. But the bull was so popular—it was allegedly the first to gore two people at once—it was bought as soon as it was killed in the ring.

Sean's going back next year. If he doesn't complete something, he's got to keep doing it until he does. At first, I said there's no way I'm going to run again. But I might.

Expert Analysis: That turn is called La Curva, and it's one of the most dangerous parts of the encierro. Bulls often crash there. When they get up, they can go left or right, and they're also separated from the herd, which makes them doubly dangerous. That's why the turn is nicknamed Hamburger Corner. Beginners should not run there. Also, you should never run with a teammate. When the bulls are near, too much is happening for you to think about anyone else. Just focus on yourself and swap stories about your exploits over a beer later. —Gary Gray, visiting professor at Penn State University and author of Running with the Bulls