Prey Drive is the desire to chase and catch moving targets.
In nature these targets are live prey: rabbits, squirrels, cats, and birds. In dog sports the targets are most often tug toys, balls, or discs.
Triggering Prey Drive is important in the game of disc dog freestyle. Moving the target away from your dog quickly and aggressively is key to triggering Prey Drive. Your dog should view the disc as an opportunity that is likely to get away if it is not pursued, so present discs that way. Targets should pop into existence and then quickly move away.
Chasing prey is an opportunity. You can’t give the dog the toy and expect it to trigger Prey Drive.
Most chases of rabbits, squirrels, cats, and birds, result in no biting on the target. It’s possible, but the target is most likely going to get away. Trying to keep it from getting away, that is the game.