Quick, here's a quiz about your Jewish knowledge. Don't worry, it won't be too difficult. In fact there is only one question.

The primary ingredient(s) of matzah, the unleavened bread Jews eat on Passover, is:

a) Flour and water
b) Human blood

If you answered (a), flour and water, you are correct. (In fact, Judaism prohibits us from eating any blood whatsoever, not to mention specifying which kosher mammals, such as cows and chickens, we can eat. Human beings definitely didn't make the list.)

Yet the truth didn't stop generations of Christians in Europe from persecuting Jews based on the false "blood libel" accusation that they kidnapped and killed Christian children to use their blood in matzah.

This sounds crazy, right? Surely no one would believe such outrageous slanders today.

Not so fast. Egyptian television recently broadcast an incredibly popular miniseries, "Horseman Without A Horse," that contained a number of slanders against Jews and Israel, including the ancient blood libel, updated. This time, instead of murdering Christian children for their blood for matzah, the nefarious Jews were murdering Muslim children for the same reason.

Okay, one might say, this heinous slander that Jews murder little kids for their blood for matzah might still be believed in some corners of the world, but it's easily disproved. After all, it's pretty clear that the Torah gives a specific recipe for matzah (flour and water, nothing else), and elsewhere prohibits murder and eating non-kosher things like human blood.

But now there's "proof." From Prof. Ariel Toaff, the son of Rome's former Chief Rabbi, no less. Toaff wrote a 1997 book in which he mused that perhaps, since so many Christians said so, Jews did in fact murder innocent Christian children.

In other words, if enough people believe an outrageous slander, it becomes inconceivable that there's no truth in it, right?

Toaff's book sparked an uproar in Italy and elsewhere. Toaff's father's successor, the Chief Rabbi of Rome, joined other prominent Italian Jews to release a statement asserting the obvious, that "A Jewish tradition of this kind has never existed, nor has any indication or custom that allows the ritual use of human blood. The only blood ever spilt was that of many innocent Jews, massacred on the basis of unjust and libelous accusations."

Ariel Toaff himself tried to halt further editions of his book so he could change the passages where he discussed blood libels, but the damage was done. You might know that your Manishevitz contains just flour and water, as the label indicates, but to many people, that's not so.

In fact, those who believe that Jews do go out and kill Christian or Muslim kids to make their matzah have millions of supporters around the world, television shows, songs (one of the ancient hymns in the traditional English cannon is an old ballad about blood libels) to back them up, not to mention the scholarly work of a prominent Jew who supports their position.

So who is wrong?

It can be Hard to Stand Up for Truth.

When it comes to the crazy accusations of the blood libel, most of us would have no trouble saying they're wrong, and anyone who believes in them is a crank.

But what about situations where when we stand up, we are labeled the crank?

Incredibly, there are cases where the lie is so widely believed, that anyone seeking to stand up to it enters a looking-glass world where truth and reality are stood upside down.

I remember watching in horror in September 2000, as first French and then international television stations broadcast a video of a terrified boy being shot by unseen Israeli soldiers. The boy, Mohammed al-Dura, immediately became an icon.

I'm a staunch Israel supporter, but I was ashamed by this video. Others carried their horror further. A month later, terrorists struck a religious school in Jerusalem, citing revenge for Mohammed al-Dura as their motive. Some countries issued postage stamps with the iconic al-Dura picture on them. Many terrorists over the years (including those who murdered Daniel Pearl) have specifically cited Mohammed al-Dura as their motivation for murdering Jews.

Incredibly, it emerged years later that the al-Dura video was a hoax, staged by local activists, and carefully edited by France's Channel-2 television station, which to this day has refused to release the full, un-doctored video, despite a French judge's requests. (See Backgrounder Mohammed al-Dura: Background of a French Media Scandal.)

Yet it can be difficult even now to stand up for the truth. The pendulum of public opinion has swung so far against Israel in some quarters that even pointing out the evidence against this iconic video risks gaining a label as a crank.

"Dueling Videos"

When did the truth become something not to delve into and find, but to debate and fight over like a boxing match?

Insidiously, today, those who are interested in the Middle East often forgo reasoned inquiry and debate in favor of competing narratives.

A startling example of this is the recent, and much discussed, UN report on Israel's actions in the 2009 war in Gaza. Many have criticized the report, written by South African Judge Richard Goldstone, as biased against Israel. One would expect Judge Goldstone, long a critic of Israel, to himself defend his report.

Yet, amazingly, since its publication, even the media-savvy Goldstone has been startled at the nastiness and take-no-prisoners attitude of many of Israel's critics.

Speaking of the eventual report which the UN Council on Human Rights issued, based on his work, Goldstone said "The draft resolution saddens me as it includes only allegations against Israel. There is not a single phrase condemning Hamas as we have done in the report."

Tragically, it seems that the truth matters less and less; political sympathy can be won by the side putting forth the most compelling narrative. In a world obsessed by spin, truth gets sidelined.

Thus, the front-page headline of the New York Times on June 2, 2010, covering the "Freedom Flotilla" convoy, which attempted to break Israel's blockade of the Hamas-controlled Gaza strip, which resulted in a firefight with Israeli soldiers: "After Sea Raid, Dueling Videos Carry on Fight."

No matter that many of Israel's critics have a long history of using doctored or even completely fabricated video footage. In this new media milieu, public opinion is king. Truth gets trampled.

The "Freedom Flotilla" was smart. It might be motivated by anti-Semitism (its founder Greta Berlin, told the New York Times that she is "the most qualified 'anti-Semite'"), but it understands that a David and Goliath story will gain more traction than reasoned argument. The Freedom Flotilla claims it wants to improve the lot of ordinary Gazans. Yet it chooses not to reason with them to stop supporting Hamas, which remains committed to Israel's destruction and consistently launches rockets from Gaza into civilian centers in Israel.

The Freedom Flotilla claims it wants merely to deliver banned supplies to Gaza. Yet it spurned Israel's offers to deliver the aid they carried overland into Gaza. The real goal of this rag-tag bunch of Hamas sympathizers on the Flotilla's ships was inadvertently revealed by a board member of the Turkish organization that funded the project. Rather than lamenting the fact that his aid didn't get through, the board member, Omar Faruk, instead rejoiced: "We became famous; we are very thankful to the Israeli authorities."

When truth matters far less than weaving a compelling narrative, what can we do? Fortunately, a number of sites, resources and organizations counter some of the most common slanders of Israel and keep us apprised of some of the most vicious lies and innuendoes concerning Israel.

I had meant to conclude this article with an uplifting quote from the Torah about the primacy of truth. But so great is my despair at the vile lies directed against Israel that I'm almost tempted to end on a far different note, and quote the murderous Nazi Joseph Goebbels: "If you repeat a lie often enough, people will begin to believe it."

On the other hand, the Talmud (Bava Batra 12a) says, "A wise man is greater than a prophet." Commenting on this, the Rebbe of Ropshcitz said "Because a prophet foresees the future, and a wise man sees the present."