The Pope has warned against getting into arguments with the Devil, who he insists is a real person.
Speaking with an Italian Catholic broadcaster, Pope Francis stated the obvious - "he is evil" - and perhaps the less-so.
"He's not like mist. He's not a diffuse thing, he is a person," Francis told TV2000, according to UK paper The Telegraph.
"I'm convinced that one must never converse with Satan - if you do that, you'll be lost. He's more intelligent than us, and he'll turn you upside down, he'll make your head spin."
He said it can be hard to know when you're dealing with the Devil.
"He always pretends to be polite - he does it with priests, with bishops. That's how he enters your mind.
"But it ends badly if you don't realise what is happening in time. We should tell him, 'Go away.'"
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Satan's appearance is never described in the Bible, so it's not clear how one is supposed to know the difference between a polite, well-meaning human and the Prince of Darkness.
His advice comes not long after he said the Lord's Prayer needs reworking, because it's not God who leads people "into temptation" - it's, you guessed it, the Devil.
He blamed a bad translation from the original Greek used in the New Testament.
"It's Satan who leads us into temptation, that's his department."