From a few kilometres across town, the blast sounded like a muffled thump - the grim reality of an explosion going off inside a packed crowd.
Sitting under fruit trees in a beautiful garden in Sanaa, my Yemeni companions looked up from their cups of tea and waited for the sound of gunfire to follow.
When they did not, we all settled back into our conversation.
We had no idea from our leafy oasis that the worst single terror attack in Yemen's history had just occurred.
Within 30 minutes, we were driving back to our hotel crammed into the usual chronic traffic. The sound of ambulance sirens screamed past us.
An al-Qaeda suicide bomber had just pulled off a ruthlessly symbolic attack at a rehearsal for Tuesday's National Day military parade.
The parade was supposed to celebrate Yemen's unification since 1990, when a war between the north and south ended in northern victory.
But the southern secessionists have been replaced by a more modern, more menacing group pulling Yemen apart: Al-Qaeda in the Arabian Peninsula (AQAP).
Their local affiliate, known as Anshar Al Shariah, later claimed responsibility for the attack in a message sent across the capital of this less-than-unified Arabian Peninsula nation.
The attack was set against the backdrop of a raging war in the southern provinces of Yemen. Al-Qaeda fighters have taken advantage of almost a year and a half of political chaos to grab swathes of the country there.
To the alarm of Western security concerns, al-Qaeda was taking ground, invading cities and getting close to their dream of their own Caliphate. Yemen, in fact, was looking like the group's biggest success story in recent years.
Since Ali Abdullah Saleh was forced to resign as president and hand power over to his deputy, Abd-Rabbu Mansour Hadi, however, the fight against al-Qaeda has been stepped up enormously.
Targeted drone strikes and a fresh offensive have been attributed to US military co-operation.
The American government has not confirmed it is carrying out the current targeted air strikes against the fighters, or that it has sent military advisers to help Hadi fight AQAP.
Strength or desperation
Monday's attack could be seen as either a sign of strength or desperation by the group.
They have lost hundreds of fighters in recent weeks to the fighting, according to the Yemeni government, and have been pushed back from some of their territories in the south.
So, these attacks are in many ways revenge against the government.
They also clearly show the strength of the group, carrying out an attack right in the centre of the capital, literally metres from a main military base and down the street from the presidential palace.
A few hours after the attack, reports circulated of two other would-be bombers found hiding in a park nearby.
What was a huge blow at the heart of Yemen's new government and military, could have been even bigger.