He will ask you for advice on how to boil his eggs next time.
That's almost correct, because they might want to take closer look at you to see why they failed.
Truth however, is that according to their doctrine a Catholic egzorcist is by profession required to distinquish between obsession by the devil and mental illness.
However since they already failed, to cover up their failure they declare you mentally ill person and do all what's in their power to force you into mental hospital.
This way if somebody points a finger at them for their failure (which is very uncommon btw.) they can point their finger at mental illness.
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However shall their egzorcism succeed they would happily point a finger at the devil even if it was mental illness to blame.
Historically speaking (in times of Jesus and before) there were no doctors to treat mental illness, so egzorcisms were always successful at the expense of mental health of a person being egzorcized.
That's why today egzorcisms are so rare, and can easily fail. (and are much more shameful for the church due to mass media and internet) so they rather avoid it or do it secretly.
