Mr Willis, the vicar of Bridlington, wanted to pass on some of the things he had learnt in his ministry to younger priests.
He says there are six classes of supernatural phenomena which a priest may come across in his work.
Firstly, there are ghosts. Mr Willis, 64, says one in ten of the population has seen a ghost or apparition. There is no doubt they exist, he says. The only question is what they are.
Some places, he says, are haunted, but not by ghosts as such.
There may be a cold spot in the room or people may feel themselves tapped on the shoulder in an otherwise empty house. Objects can move without anyone being seen to move them.
Poltergeist disturbances are similar but centred around a particular person. "There are people who can look at objects and they move - this has been filmed in a laboratory."
Poltergeist activity, he believes, is caused by people who relieve emotional stress subconsciously by moving physical objects at a distance. Mr Willis is one of the nine diocesan exorcism advisers appointed by the Archbishop of York, Dr John Habgood, who is regarded as the most scientifically literate bishop in the country.
Most of their work involves praying, and Mr Willis plays down the dramatic images of popular imagination.
He says he is sometimes asked to deal with evil presences. "A certain patch of the woods, a crossroads or a room may have an atmosphere. Animals can sense it. But that brings us to the whole problem of evil and how it can possess anything. Does it have intelligence?"
The last, and perhaps the largest category comes, he says, from people interested in the occult. Witchcraft was only made legal in Britain in 1951.
But now, he says, "there are astrologers, Ouija boards and fortune-tellers all over the place".
"People who have dabbled in that stuff will come along to me and say they are absolutely possessed by a sense of evil", Mr Willis said.
"You don't get possessed walking to the supermarket, but if they call evil into their lives..."Reuse content