What does the rocking horse symbolize?

The rocking-horse which Paul rides in order to ascertain the winners of horse races is a mysterious object embodying many inversions of reality. The wooden rocking-horse is not an actual horse, and yet it represents a horse. Also, rather than racing forwards like a real horse, the rocking-horse can only rock back and forth in place. In that sense, it is perhaps more a symbol for race gambling rather than horse-riding itself. As such, Paul is not a jockey when he rides the horse. The horse does not take him around the racetrack to a successful finish line but rather further and further towards the gambler's self-destructive goal.