http://en.allexperts.com/q/Horse-Rac...ling-filly.htm
"When a thoroughbred is in fight/flight mode they can often kill themselves, as well.
Not intentionally, but they do tend to lose all sense of self preservation
when they feel the need to escape badly enough."
Instinctual behavior, HARD WIRED, will trump the higher centers of "learned logic" that animals with higher developed brains can come to trust
Read Konrad Lorenz
ON AGGRESSION, or Desmond Morris
HORSEWATCHING.