Possible Clues:

• Sound of hoofbeats
• Bygone street sound
• Sound of coconuts in 'Monty Python and the Holy Grail'
• Sound reproducible with coconut shells
• Sound of horse's hooves
• Noise of a horse's hooves
• Sound of horse caught between cuts
• Sound of a horse's hooves
• Sound of stock footage?
• Sound of horses' hooves