WASHINGTON -- Friday morning, a madman attacked more than 20 children at an elementary school in China. As of this writing, there are no reported fatalities.
A few hours later, a madman attacked an elementary school in Connecticut. As of this writing, 20 of those kids are dead.
The difference? The weapon. The madman in China had a knife. The madman in Connecticut had semi-automatic pistols.
Look up Wikipedia's list of the worst school massacres in history, and you'll see the pattern. Madmen are everywhere. They strike without regard to gun laws, mental health care or the national rate of churchgoing.
They've slaughtered children in every country you'd think might have been spared: Scotland, Germany, Canada, Brazil, Finland, Japan.
They've falsified every pet political theory about what kind of culture or medical system or firearms legislation prevents mass murder.
But one pattern holds true: The faster the weapon, the higher the body count.
It's not politics. It's logistics. If you stick a knife in your first victim, it takes time to move on to your second victim.
You might need two stabs or more to finish off the first kid. By then, the other kids have begun to flee. Soon, the cops will be here.
How much time do you have? At some point, it's time to off yourself.
And all you managed to kill were two kids because the only weapon you had was a kitchen knife.
Google "knife control" and you'll find legions of gun-control skeptics comparing U.S. firearm attacks to Chinese knife attacks.
In the past two years, there's been an epidemic of knife attacks on Chinese schools.
Some of them show up on Wikipedia's list of school massacres. But none crack the Top 10 because the body counts never rise above single digits.
It's just too hard to kill that many people, even little kids, with a knife.
Guns do more damage. Look down the list and you'll see gun after gun after gun.
But not all guns are equal. I've gone through the 25 worst massacres on the chart, and nearly every shooter had a semi-automatic weapon.
The one exception was a guy who had speed-loaders and a bandolier so he could keep firing.
The shooter in Connecticut reportedly had used Glock and Sig Sauer semi-automatic pistols and possessed an assault rifle that could fire as many as six bullets per second.
High-capacity magazines are another common factor.
All these patterns converge on a common lesson: Speed kills. Madness pulls the trigger, but the rate of fire drives the body count.
It's not all about guns, either.
The worst Chinese school massacre by a knife-wielding madman wasn't caused by the knife.
The perpetrator used the knife to scare the kids and make them retreat to the back of a classroom. Then he locked them inside and killed them by starting a fire.
Right below him on the list is a guy in Germany who killed one victim with a lance and the rest with a flamethrower that he used to ignite a classroom.
Knives and lances take too long. It's more efficient to kill everyone at once.
That's what the record-holder did: He wiped out more than 40 victims with a series of bombs in 1927.
I wish we could pass a magic law that would stop madmen from killing our children.
We can't. There will always be angry lunatics. There will always be knives and shotguns and gasoline.
I don't think banning guns will make the problem go away. We don't need another all-or-nothing war between pro-gun and anti-gun ideologues.
What we need is a frank, precise, constructive conversation about the problem of weapons that fire at high speed.
You don't need rapid-fire weapons to hunt or defend your home.
Cops don't need them to shoot down bad guys.
And while it's true that passing a law against them won't eliminate them, that's not an argument against legislation. It's an argument for going beyond legislation. The community of gun sellers and enthusiasts must act collectively to track and control the technology of mass murder.
Every child who died in that school in Connecticut Friday was precious. To lose even one young life in such a senseless way is a gut-wrenching tragedy. But this I know: It didn't have to be 20.
William Saletan covers science, technology and politics for Slate. Twitter: @saletan