Why might there be an option jump? First, when it comes to speed, you might have a more difficult but direct option and an easier but longer option. A more experienced horse and rider might choose the direct route while a less experienced horse and rider might decide to play it safe and take the slower route. The difficulty could be in the height, width or type of jump. A spooky jump such as a liverpool or a dry ditch could be used on the faster track while a straightforward oxer or vertical provides the safe option.
In a schooling class, including option jumps might allow the course designer to provide opportunities for the more advanced horses to school over open water or something similar without requiring everyone to jump it.
How will you know if there are options in your course? First, look on the course diagram to see if there are two jumps with the same number in the course. There should also be "option," written between them. When you walk the course, look for jumps near one another that are both flagged and have the same number.
What happens if you have a refusal or run-out at one of the options? You are allowed to take the other option for your second attempt, although you must wait for the initial jump to be reset if you have dislodged it.
Here is the official EC rule for option jumps:
FEI ARTICLE 215 ALTERNATIVE OBSTACLES AND JOKER
1. When in a competition two obstacles of the course carry the same number, the competitor has the choice of jumping either one of the obstacles:
1.1. if there is a refusal or run-out without a knock-down or displacing of the obstacle, at his next attempt the competitor is not obliged to jump the obstacle at which the refusal or run-out occurred. He may jump the obstacle of his choice;
1.2. if there is a refusal or run-out with a knock-down or displacing of the obstacle, he may only restart his round when the obstacle knocked down or displaced has been replaced and when the Ground Jury gives him the signal to start. He may then jump the obstacle of his choice;
2. Red and white flags must be placed at each of the elements of this alternative obstacle.