The phrase suggesting that a "real horse's skull is used in the play", while from a human's viewpoint could be considered true, I do believe to be false. The horse's skull actually uses the play...................

A very strange tradition this Souling, with many strange occurrences every year (soulers mysteriously falling down towards the end of an evening, mad laughter heard coming from behind hedges along the way etc) and many of these are to be observed at the Last Night of The Play, November 7th.

Come and see me, the Horse, in all my pomp.... 2100, Saracen's Head, Warburton.