Which grooming tool is effective for removing dirt from a grass-kept horse?

The curry comb is particularly effective for removing dirt from a grass-kept horse due to its unique design and function. It has a textured surface that helps to loosen dirt, debris, and loose hair from the horse's coat. When used in a circular motion, the curry comb not only removes dirt but also stimulates the skin and promotes the production of natural oils, which can lead to a healthier and shinier coat.

As for the other tools listed, while they each serve important purposes, they are not specifically designed for the same function. A body brush is more suitable for removing dust and fine particles from the coat after the majority of dirt has been loosened with a curry comb. It can clean the coat to a shinier appearance but is less effective at dislodging caked mud or grime. A hoof pick is designed primarily for cleaning out the hooves and does not address the horse's coat. Lastly, a soft cloth can be useful for specific areas or for polishing the coat but lacks the necessary rigidity to effectively remove dirt and debris from a grassy environment. Thus, in the context of grooming a grass-kept horse, the curry comb stands out as the best option for effective dirt removal.