It was near the end of their historic, two-hour public encounter that the former US diplomat, Mr Barry Rosen, came closest to losing his temper. Mr Abbas Abdi, one of the masterminds of the 1979 storming of the US Embassy in Tehran, claimed their hostages were not badly treated - why, he recounted, the diplomats used to play chess with the Iranian students.
Mr Rosen's voice rose with suppressed fury. He was held alone in a dark cell for most of his 444 days as a hostage, during which he saw sunlight only three times.
"The American hostages did not sit down and play chess with the students," he said angrily. "That was a pure fabrication. To give the impression that we were treated well by the hostage-takers is wrong."
But the meeting between Mr Rosen and Mr Abdi here on Friday went beyond the dramatic reunion of a hostage and his captor. It marked the first follow-up to conciliatory statements by President Mohamed Khatami of Iran last January, and the US Secretary of State, Ms Madeleine Albright, and President Clinton in June.
"I am convinced that two decades of animosity between our two countries is coming to an end," Mr Rosen said.
Both men stressed they had come to Paris as private citizens, not as representatives of their governments. Yet each looked and spoke like a caricature of his own society.
In his dark suit and tie with carefully-groomed beard, the balding Mr Rosen (54) resembled very much the diplomat he once was. The US Embassy press attache in Tehran when the Iranian revolution took place in 1979, he now works at Columbia University in New York.
Mr Abdi (42) may be an influential editor at Salam newspaper now, but he still has the aura of an Iranian revolutionary - tinted spectacles, open-neck shirt, several days' growth of beard.
As a student at the Polytechnic University of Tehran in the 1970s, Mr Abdi belonged to the "line of the Imam", which believed the empowerment of the poor was the most important of Ayatollah Khomeini's teachings. In the 1980s, this faction advocated the taking of western hostages in Lebanon and the assassination of the regime's opponents abroad.
It is a measure of the extraordinary changes that have taken place in Iran in recent years that a former radical like Mr Abdi is now an enthusiastic supporter of President Khatami, who advocates respect for human rights, tolerance and rapprochement with the West.
Although Mr Rosen and Mr Abdi both said they want government-to-government contacts, their closing handshake was frosty. The meeting showed how far the US and Iran have to go before they can fulfill Mr Abdi's wish of returning to the relationship they enjoyed before the 1953 Anglo-American coup against the democratically-elected government of Mohamed Mossadegh.
Each felt his country was the wronged party, that the other had to make the first step.
Mr Abdi's speech was a litany of US wrongs against Iran. "The seizure of the US embassy in Tehran was the most non-violent reaction (to the Shah's receiving asylum in the US) that could have taken place," he said. "If we had not done it, armed groups would have attacked the embassy . . . which would have led to the murder of some Americans."
For Mr Abdi, holding 52 diplomats hostage for 444 days was not comparable to "holding an entire country hostage for 25 years".
"Reconciliation cannot involve establishing who did what to whom and when," Mr Rosen answered. But a few minutes later he said differences could not be settled "until the Iranian people accept the fact that the hostage crisis was a moral and ethical issue in which the rights of other human beings were violated."
He maintained the US had done some good things for Iran - "it did protect Iran from the Soviet grip."
The meeting also underscored divisions between Iranians. Four times Mr Abdi was interrupted by Iranians in the audience who accused him of a role in the execution of tens of thousands of Iranian political opponents exactly 10 years ago.
The war with Iraq had just ended and thousands of fighters from the opposition Mujahedd in Khalq invaded, believing they could topple Ayatollah Khomeini. In its panic, the revolutionary leadership murdered at least 20,000 prisoners.
I was surprised to find Zoreh, an Iranian woman who works in a shop near my home, in the audience. She was trembling when she grasped my hands.
"I wanted to see his face," she said of Mr Abdi. "My brother and sister were killed under his orders. My mother and I waited three months outside the prison. In November 1988 they gave us my sister's handbag and said, `They are dead. Go away now.' No bodies, no grave."
Mr Abdi said the allegations were "most unfortunate" and the result of "a very big misunderstanding".
Yes, he had worked for Iran's chief prosecutor in 1988. But his work was in social research, and the prosecutor did not decide on the executions.