Saw a coconut smoothly in half. It's important that the edges be flat. There is milk in the coconut so saw partway through the coconut, remove the saw and pour the milk into a pan or in the sink. Replace the saw in the slit and finish cutting the coconut in half.
Attach hand straps by screwing any solid strap into both sides of the coconut half with the drill. Center the strap and leave enough room for your hand to comfortably, but snugly, fit under the strap.
Select the appropriate surface to strike against, based on the landscape the horse is galloping on. Use a box of gravel, sand or leaves, a wooden floor, or improvise to imitate the sound of galloping on cobblestone streets.
Slip your hands into the hand straps on the coconut halves.
Use the coconut halves to strike your selected surface in a three-beat rhythm. One solid beat followed by two rapid beats in succession will best imitate galloping.