The correct answer is: so the seeds can survive the mechanical forces and conditions in an animal's gut. Some plants produce edible and fleshy fruit specifically so that animals will assist in seed dispersal by eating the fruit. However, this strategy would be pointless if the seeds are destroyed in the animal's gut. The seeds would have to survive the mechanical chewing action of the animal's teeth, as well as the highly corrosive environment of the animal's gut. This is why seeds of fleshy fruits tend to have tough and hard protective coats.