Similar to the seemingly ridiculous superstition in Anglo countries that being crapped on by a bird is good luck, the French have their own animal faeces-related irrational belief. Theirs is that if you step in dog poo with your left foot, it brings you a slice of good luck. However if it's the right, you're doomed. Perhaps this explains why Parisians are so lax about letting their mutts foul the pavements of the French capital.