When all natural explanation for a persons behavior is weighed out, the priest must observe the person for any signs of supernatural evidence. Fr. Gary Thomas – one of United State's most renowned exorcists – lists some of the examples as what the Church would consider to be supernatural evidence:
"A knowledge of hidden things...so people who know something they have no reason to know, either about me or a situation or to predict the future" (qtd. in Coffin).
"Being able to speak in a language they have no competency in...usually occur either in [a] deliverance prayer or a formal exorcism" (qtd. in Coffin).
"The person possessing inordinate strength – that will often come out in an exorcism in cases where the demon is very violent" (qtd. in Coffin).
"The person can have very extreme facial contortions and a change in the voice. Sometimes their whole body language, including their face, can take on the look of a reptile or a snake, and I've had that happen a number of times" (qtd. in Coffin).
"The use of holy water or placing a crucifix on a person can cause a sensation of burning" (qtd. in Coffin).