Reports that the Syrian military is preparing chemical weaponry raise a challenging question: why? For what rational reason would the Assad regime be readying stocks of sarin gas?
On the basis of intelligence findings, western leaders are speaking out on the subject this week. Hillary Clinton, the US secretary of state, said the use of chemical weapons would cross "a red line for the United States." Anders Fogh Rasmussen, the secretary-general of Nato, promised "an immediate reaction". And President Barack Obama warned Damascus that "there will be consequences". That chorus of voices suggests an increasingly robust front against the regime in Damascus.
The story first broke in The New York Times that the regime appears to be preparing stocks of sarin, a colourless, odourless nerve toxin invented in Nazi Germany. Sarin was prominent among the poisons used by Saddam Hussein during the Iran-Iraq war, and Saddam used it again in the 1988 attack on Halabja, in Iraqi Kurdistan.
Syria, one of only eight UN member states that have not ratified the UN-sponsored Chemical Weapons Convention of 1997, is known to have the precursor chemicals that are combined to make sarin.
But what would be the point of using it now? The history of chemical weapons reveals them to be hopelessly impractical in close combat, risky to store and dangerous to your own troops.
More importantly, the Assad regime has already proved to the world that it is willing to kill Syrians without regard to their combat status, age, or gender - just the way chemicals kill. The regime is already thoroughly disgraced, although the use of sarin might indeed provoke an international military response and possible war-crimes charges.
The apparent military progress by the rebels raises the possibility that sarin-stirring is merely a bluff. The leak to The New York Times might also hint that western powers are paving the way for a stronger response to the violence. The rebel victories may push outside powers to look for an opportunity to get more involved before the regime collapses.
Inevitably, a western "red line" over these weapons evokes memories of George W Bush's notional "weapons of mass destruction" in Iraq. A report like this one, last July, seemed to be a false alarm - the chemical precursors were reportedly being moved for safekeeping. All in all, it's not possible to be perfectly sure about the weapons now.
We can be sure, however, that the Assad regime has been murdering Syrians and destabilising the region for almost two years. The chemical-weapons threat is a worrisome addition to the mix, but shouldn't distract from working towards the day when the regime doesn't have any weapons at all.