Shape-shifting in the Irish identity

"I myself when I was a boy of ten or eleven, was perfectly convinced that on a fine dewy morning in summer when people were still in bed, I saw a strange horse run around the seven-acre field of ours and change into a woman, who ran even faster, and after a couple courses around the field disappeared into our haggard.  I am sure, whatever I may believe today, no earthly persuasion would, at the time, have convinced me that I did not see this.  Yet I never saw it again and never heard of anyone else seeing the same."

The Fairy Faith in Celtic Countries

~W.Y. Evans Wentz