In the Rhyme Humpty Dumpty, Why the heck would a horse try to put back together an EGG? How could it?

Some nursery rhymes were derived or associated with historic events (i.e. London Bridge & Ring a Ring o' Roses), If humpty dumpty meant anything other than an egg. Why the heck would a horse try to put it back together? Or what the horse could have meant in any other interpretation.