david viewing, excellent post
In my experience, horses are designed to run away from sabre-toothed tigers and take very little notice of aeroplanes, even low fast jets. Show them a hedge with a paper bag in it and it's another matter!
Very true. Have seen my other half's horse totally ignore an F-15 that blazed overhead at about 1000ft with burners lit, but if she comes round the corner of the stable yard to find a Chipmunk (dH, not Yank squirrel) parked up on the grass quietly minding its own business... time to run for your life.