Terms and conditions for Twitter users are very contested but it is fair to assume that hostage-bartering on the platform is prohibited. That did not prevent the Iranian Foreign Minister Mohammad Javad Zarif from using the US social media site to make threats last week.
Mr Zarif, who continues to cling to a reputation as an English-speaking moderate in Tehran, published the terms of his country's interests in exchanging prisoners. Writing in the midst of a series of releases that saw Sirous Asgari and Majid Taheri deported from the US and Michael White sent home from Iran, Mr Zarif was blunt.
“Pleased that Dr Majid Taheri and Mr White will soon be joining their families,” he wrote. “Prof Sirous Asgari was happily reunited with his family on Weds. This can happen for all prisoners. No need for cherry picking.
“Iranian hostages held in – and on behalf of – the US should come home.”
That last line was an attempt at an inverted blame game, a classic tactic so standard of Iranian diplomacy. It should not fool anybody. There can be little doubt Mr Zarif was fully focused on collecting political concessions for his regime's bargaining chips.
By contrast to this meanness of spirit, it was heartening to hear Mr White speak. On the tarmac at a Swiss airport, he spoke of his recovery from Covid-19 and his hopes to get to Disney World when he reaches America.
It took me back to my first memories of news reports about hostages being held in Lebanon and Tehran in the early 1980s. It was a huge international story. The plight of the westerners held in Beirut dominated many news cycles. The anguish of the relatives and the dangers of the city were always dramatic interludes, related in many gripping reports.
Over the decades, the Iranian regime has had an almost exquisite interest in leveraging hostages for its foreign policy goals. The practice has proven to be a route to advancement for ambitious officials. Among those who oversaw the US embassy siege was a future president of the Islamic Republic, Mahmoud Ahmadinejad.
When it seized 15 British soldiers on the Shatt Al Arab river near Basra in 2007, Iran was isolated and under pressure, as it is now. It had a particular goal. At the start of the year, Britain’s American ally had seized a handful of Iranian operatives in Erbil, Iraq.
Over the course of 10 days in Tehran, I watched the negotiations and pressure game play out over the fate of the military personnel. They were mostly young people. They had no particular strategic value as individuals.
Every day as the outcry for their release grew on Tony Blair's government, Iranian officials delighted in the impasse. For cover they would cite the 1975 Algiers Agreement – a deal between Iran and Iraq to settle their border disputes and conflicts, which had split sovereignty on the Shatt Al Arab estuary – and claim the patrol had crossed the line.
Finally the Iranians felt the point had been made. By that stage even the Pope in Rome had intervened to plea for a concession. When I flew out on the plane with the released crew, no one was under any illusion of the real goal for the Iran. It had proven it had cards to play.
The myth of friendly western-educated Iranian leaders pushing gradualist policies to change Iran has been consistently rendered bankrupt by these episodes.
The current hostage crisis began in earnest at the same time as the 2015 nuclear agreement came into force. Brian Hook, the US envoy on Iran, spoke at an event in London last week in which he highlighted Europe’s serious issues with hostages in Iran.
The British citizen Nazanin Zaghari-Ratcliffe told her husband on Friday of her despair after four years as a prisoner in Iran. While she is on parole at her parents' home in Tehran, Ms Zaghari-Ratcliffe still awaits word on a clemency decision that her supporters had hoped would come by Eid Al Fitr.
According to her husband, Richard, Ms Zaghari-Ratcliffe is now convinced she is being held until Britain sends back £400 million (plus interest) that the government of Mohammad Reza Shah Pahlavi paid London for tanks in 1978, a year before the monarchy was replaced by the Islamic Republic.
On the anniversary of another arrest, Emmanuel Macron made a plea on Friday for the release of Fariba Adelkhah, a dual national who is being held in Tehran. Anne Hidalgo, the mayor of Paris, put Ms Adelkhah's portrait on the facade of the city hall with the slogan: "Her fight for freedom is ours."
While she is still serving five years, her French partner Roland Marchal was freed in March. He was sent back after French authorities released Iranian engineer Jalal Rohollahnejad.
The steady drip of quid-pro-quo releases only really reveals why people have been seized in the first place. Arrests by the regime bear no like-for-like comparison.
All parts of the Iranian hierarchy are engaged in this human bartering. It is happening on a scale unseen anywhere else in the world. It is fair to say that the Islamic Republic pawns people for its strategic goals.
Damien McElroy is the London bureau chief of The National