One of the men in this picture is not actually a real cardinal - but can you spot which one?
If you can pick the imposter who infiltrated a top-secret meeting, then you will be doing better than a group of bona-fide cardinals and the Swiss Guards whose job it is to protect the Pope.
The task of picking a new leader for the world's billion-plus Catholics briefly descended into farce when a man wearing a scarf wrapped around his waist mingled with senior clergy and chatted with priests.
Referring to himself as Basillus, he told them he belonged to the "Italian Orthodox Church," which does not even exist.
Eagle-eyed cardinals spotted that the crucifix around his neck was also highly unorthodox. Also, the cassock he was wearing stopped short of regulation length around the shoes.
His disguise crumbled and he was eventually seized by Vatican guards who removed him from the scene. It is unclear how long he loitered undetected.
The cardinal and the hot pants
It emerged the man is called Ralph Napierski and he has appeared in public wearing clerical robes before.
One picture depicts Napierski cudding up in public to a woman who is semi-naked, wearing only hot pants and a big smile.
However a Vatican spokesman told Reuters news agency that the infiltrator had not taken part in any behind-closed-doors discussions on his latest prank.
He said: "Everyone seated for the congregation is a real cardinal."
All eyes in the Catholic world are on Vatican City, as 117 cardinals elect a successor to Benedict XVI. It is hoped the conclave will make a decision in time for the new pope to preside over Holy Week.
The pontiff resigned last month, becoming the first pontiff to quit the post in 600 years.