They run away or bolt.
When a horse is frightened or afraid their first instinct is to Flee, run or get away. known as spooking.
A horse's first instinct if it is afraid is to run.
to bite
Bolt.
To run
flight or fight and if it is afraid it is going to have a flight instinct
Scatter in groups.
run away
Horse will Flee
For Howrse it's answer is Flee.
First it will flee.
flee