Every time I see that, it drops my jaw. I found some interesting words by Huaso's rider (Alberto Larraguibel Morales) about that jump:
"On the first try, I miscalculated the distance and allowed the horse to refuse. If I had then applied the whip, the horse would had become nervous, because an animal understands when it's being asked to perform above his capabilities. In the second jump, I must have made a mistake of a centimeter or so, because Huaso passed the hands but touched with the belly and the hinds, and knocked down the obstacle... there was only the third and last attempt left. I recalculated again, and in the precise moment we flew... The most difficult moment was the apex of the jump. My eyes were about 4 meters above the ground and I had the sensation of falling head first. My slightest tremor would have been felt by Huaso; who then would have left his hinds behind and we would have crashed together, but we went over. The moment seemed to last forever. I didn't hear a single shout and thought that something had gone wrong, but I couldn't hear the obstacles falling either..."
Here is more about the Huaso/Chileno jump-off and the "unofficial" high jump set previously (8' 3.5") - "unofficial" because there were only 25 people in attendance, but it did get caught by a photographer: http://www.youtube.com/watch?v=xhHBhc-ihOI&NR=1