If a bull comes to a halt for whatever reason during a running it is normal for the runners to try to hail the animal to get it to move forward once more. This technique should be left to the experienced runners and to the bull minders. In any case, some important steps should be kept in mind. First of all, the runners should respect the space created by the bull minders, the so-called pastores. These bull minders know how the animals behave and they will try to rouse the animals with their rods. Secondly, it is vital to try to keep the bull moving forward towards the bullring because the people in front are expecting the bull and aware of the situation. If a bull turns back it catches runners totally unaware of its presence as they are now more relaxed thinking that the bulls have all passed (Nevertheless, runners should always wait for the sound of the rocket that announces that the bulls are safely in the pens).
Hailing the bulls, as we can see in this series of shots taken by Xabi Lizarraga, should be made from the back to the front and from the start to the finish of the course. It is not possible to relate here how exactly it is done, because that comes with experience, but sometimes it is enough to circle around the space in front of the bull to prompt it to once more to run ahead and to complete the course inside the bullring.