Horse is defenceless against head-butt
The horse cannot talk and cannot explain the pain and fear experienced by that assault. It cannot defend itself in any real terms. It cannot get any comfort or reassurance.
And it can’t call in the trade union to take up its grievance. Horses are also defenceless against humans who choose to inflict pain and suffering on them — often on a daily basis as those watching a race in progress can see for themselves.