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John Keegan argues that the longbows ' main influence on the battle at this point was injuries to horses : armoured only on the head , many horses would have become dangerously out of control when struck in the back or flank from the high-elevation , long-range shots used as the charge started .
 John Keegan
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 John Keegan