The handshake: It's a ritual that goes back at least to the 5th century BCE, wherein two people, more often men than women, clasp each other's hand. Originally meant to show you held no weapon, it's used as a sign of greeting, a farewell gesture or a mark of agreement as good as a signed contract – "We shook on it."
Campaigning politicians use them until their hands bleed, and diplomats employ them as a signal of mutual respect.
But whether it's a traditional handshake, a fist bump or a high five, the one thing you don't do is leave someone hanging … not unless you mean to embarrass him.
But that's what Iranian President Hassan Rouhani did this week at the United Nations to U.S. President Barack Obama – left him hanging with his hand (metaphorically) extended, trying to offer a signal of respect to the recently-elected Iranian leader.
All week there had been rumours that the two men would meet in New York; they might arrange to accidentally bump into each other, they would at least shake hands – it would be the first handshake between leaders of the two enemy states in more than 34 years.
Perhaps Mr. Obama wanted it too much. Since his inaugural speech in January, 2009, he has said to leaders of countries such as Iran, "we will extend a hand if you will unclench your fist." So, when Iranian officials announced Tuesday that it was "too complicated" to arrange, that there would be no meeting, no handshake, Americans were disappointed, and their President looked weak.
First Congress made it clear it wouldn't back Mr. Obama's plan to launch an attack on Syria because of that country's use of chemical weapons; now this snub, by the Iranians of all people.
Looked at from Tehran, however, this missed opportunity may well have been a narrow escape for Mr. Rouhani.
While one reform-oriented Iranian newspaper, Shargh, ran a story about the handshake that never happened – "Perhaps Another Time," its headline read – a conservative paper close to Iran's supreme leader Ayatollah Ali Khamenei made it clear the Rouhani charm offensive may have strayed too far and it was good that he pulled back. The Kayhan newspaper expressed horror that "the clean hand of our President would for moments be in the bloody clench" of President Obama.
Shaking hands with Mr. Obama might have been praised by many Iranian citizens, but it would have made the country's hardliners apoplectic, it seems. As Mr. Rouhani explained later to CNN interviewer Christiane Amanpour: "we didn't have sufficient time to really co-ordinate the meeting to the full extent that we needed to."
If a simple handshake can matter so much, it's no wonder a single word – the Holocaust – can cause political panic.
In that same CNN interview, Mr. Rouhani was asked for his views on the H-word. The Iranian leader would have known the question was coming. After all, his predecessor as president, Mahmoud Ahmadinejad, was infamous for his denial of the Holocaust suffered by the Jews of Europe at the hands of the Nazis.
Mr. Rouhani appeared to choose his words (in Farsi) carefully; he knew how much was riding on his answer.
"I have said before that I am not a historian personally and that when it comes to speaking of the dimensions of the Holocaust as such, it is the historians that should reflect on it.
"But in general, I can tell you that any crime … including the crime that the Nazis committed towards the Jews, as well as non-Jewish people, is reprehensible and condemnable, as far as we are concerned.
"So if the Nazis, however criminal they were, we condemn them, whatever criminality they committed against the Jews, we condemn, because genocide, the taking of the human life, is condemnable and it makes no difference whether that life is a Jewish life, a Christian or a Muslim or what."
There it was, a ground-breaking statement. A leader of the Islamic Republic of Iran had finally acknowledged "the Holocaust," describing it as "genocide" and a "crime that the Nazis committed towards the Jews," and calling it "reprehensible and condemnable."
It may only have been a statement of a simple truth, but it was profound nonetheless. So profound that it rang alarm bells back in Tehran. The semi-official news agency Fars accused CNN of fabricating part of the interview – claiming the President had not used the word Holocaust or described it as "reprehensible" – even though the U.S. broadcaster had used an interpreter provided by the Iranian government.
Mr. Rouhani repeated the wording Wednesday in a meeting with newspaper editors in New York. This is one point the hardliners are going to have to live with it would seem.
At the very end of Mr. Rouhani's speech to the General Assembly on Tuesday another word was unexpectedly heard coming from the Iranian leader's mouth: the Torah, as in the first five books of the Hebrew Bible.
What Mr. Rouhani said was:
"As stated in the Holy Qur'an: 'And We proclaimed in the Psalms, after we had proclaimed in the Torah, that My righteous servants will inherit the earth.'"
In this one paragraph he linked Islam to Christianity and Judaism and showed them in parallel. His reference to the Psalms is to Psalm 39, one specifically ascribed to Jewish King David.
I happened to be with a group of Toronto Jews shortly after Mr. Rouhani gave his speech Tuesday night. That last paragraph was what really got their attention. "Did he really say that?" one asked in disbelief.
These people were particularly impressed that the Muslim leader said it during the Jewish week of Succot that leads to the holiday of Simchat Torah, a day in which Jews celebrate their holy book.
There are grave concerns over Iran's nuclear and foreign policies, and good reason for skepticism about the value of Mr. Rouhani's charm. But to many people, it will be the little things they remember.