The attack in Yanbu was designed to terrify the country
Saudi Arabia is not a place much given to public demonstrations - for one thing, they are illegal.
But it is also too hot to be outside for long periods in the day.
And Saudis are private people who look mostly to family and tribe; they like to know with whom they are mixing.
Most discussion and political activity takes place, therefore, behind closed doors and high walls.
It is one reason the country is so difficult to read.
The so-called "Arab street" in Saudi Arabia is the Arab sitting room.
'Propaganda by deed'
There was a rare public political demonstration the other day in the kingdom.
It took place over several hours in the Red Sea oil town of Yanbu.
There were slogans, speeches, and a visit to two schools.
The centrepiece of this event was the bloody and increasingly tattered body of a Western oil engineer being lashed to a car and dragged through the streets for all to see.
"This is the president of America," said one of four gunmen in charge of this display, as he brought the body to the car park of a local boys' school.
"God is great! Join your brothers in Falluja."
Days earlier, a statement attributed to al-Qaeda had said: "God willing, the day will come when bodies of Americans and Jews will be dragged, humiliated and trampled in the Arabian peninsula."
This "propaganda by deed" did not seem to win Saudi hearts and minds in Yanbu.
"I couldn't eat and I couldn't sleep the whole night," one of the schoolboys told the Associated Press news agency.
"I have been having nightmares."
Another said: "This thing has changed my life forever. I was shocked and terrified when I saw them.
"This is not right. This is un-Islamic," he added.
In a protracted gun battle, the Saudi police later killed all four of the gunmen.
Need for reform?
Nevertheless, after this latest violence, Western workers are debating whether to leave.
And, more widely, others are asking just how stable is Saudi Arabia and the position of the Saudi royal family?
So far, reports from the kingdom say foreigners are largely staying put... but no-one knows if that brittle resolve will survive the next attack
"I don't think they will fall. We're some distance from that," a former British ambassador in Riyadh, Sir Andrew Green, said.
"This is a strong regime. There is no serious alternative to it."
In a debate with Sir Andrew on the BBC's Today programme, Saudi analyst Mai Yamani disagreed.
"I think it is the beginning of an end, if there are no political solutions," she said.
She added that the regime had only two or three years left if it did not undertake serious reform.
The Saudi royal family gave the first hints that it would embark upon some limited, cautious reform last year with talk about human rights and the promise of local elections.
If women are allowed to vote, this may cause more fury on the part of the religious hardliners with whom the royal family has been in uneasy alliance since the kingdom was founded.
But the royal family seems split about how far and how fast to go with reform.
Some members are said to be terrified by the prospect of change.
Saudi insists it is successfully cracking down on militancy
So a number of leading campaigners for democracy were arrested recently, accused of falsely adding names to a petition calling for reform.
"The royal family are losing control of this situation. They have no... solution for this violence," Dr Yamani said.
"They are clamping down not only on the jihadis but also on the reformists.
"If they [the royal family] don't win the support of the middle class - the educated class in the country - there will be more and more people who will throw themselves into the arms of the jihadis."
Foreign worker fears
One crucial, unanswered question is how many armed militants there are in Saudi Arabia.
The authorities are claiming there are few and that they are having increasing success in hunting them down.
The many gun battles in the kingdom over recent months are explained as a result of arrest raids which flow from successful intelligence operations.
One Saudi cleric who claims links to the militants advances a different explanation.
There are thousands of the militants, he told me, and the police are being overwhelmed.
He thought that the Saudi royal family - far from crushing the militants with an iron fist as King Fahd has promised - would have no alternative but to negotiate.
In this atmosphere, the US Government advised its citizens to leave Saudi Arabia.
If American workers follow that advice in any large number, it will be a huge propaganda victory for al-Qaeda.
Tensions are high among expatriate workers in Saudi Arabia, as might be expected after the attack in Yanbu which was clearly designed to terrify.
So far, reports from the kingdom say foreigners are largely staying put.
But no-one knows if that brittle resolve will survive the next attack.