Not a reward, just a way of shifting gears. The trainer must think through the whole action of flipping backwards and figure out what is the slightest beginning of flipping backwards. We don't give a fish every time, but about one in three, and not on a routine but in a varied way. When we reward the whale everytime he performs he gets to expect the reward and when he doesn't get it, he thinks he is being punished. The tangible reward can quickly become associated with praise, patting and enthusiasm.
Intangible rewards are more powerful for people, dogs, cats, and orcas.
Mistakes didn't happen. In the Sea World tank wasted motion is ignored until the routine is fluently played by the whale. After the whale has become fluent, then the trainer ignores a sloppy routine. When an animal starts goofing off, we go back to something that is easy to do - then we reward the easier routine. If the animal is sulking and just hanging around, we may just dump in a whole basket of fish for nothing at all.