THE Facebook post was disgusting. It alleged that a leading international soft drink manufacturer (which can’t be named for legal reasons) included aborted foetal cells in its secret formula.

Leaving aside the issue of abortion, it claimed that the company was tricking its customers into becoming cannibals. Astonishingly, many people accepted this. “Why would anyone want to do this?” I asked online. No one answered.

The claim, like many others on the Internet, is now believed false. Though the odd human hair may accidentally fall into a vat, food companies go to extraordinary lengths to ensure that it doesn’t happen.

But the story does begin with a grain of truth. In this case, the soft drink company hired a research firm in 2010 to develop new flavours. And that research firm had published a scientific paper a decade ago in which it referred to using a human embryonic cell line called HEK 293. It has also mentioned the cell line in more recent patent applications.

The controversy got started last year when a group called Children of God for Life discovered the 2002 paper in the Proceedings of the National Academy of Sciences and decided that this tenuous link was grounds for a boycott of all the firm’s clients.

HEK stands for human embryonic kidney and, with the number, refers to a line of cells derived from an aborted foetus in the Netherlands in 1972. A biologist named Alex Van der Eb spliced these cells with an adenovirus, a type of cold germ, which can make a cultured line of cells immortal.

Since they have been made artificially cancerous, these cells are not much use as a model for how healthy human cells behave, but they have other advantages. They’re easy to keep alive and to work with and useful in developing drugs and vaccines.

The research firm in question had apparently modified HEK 293 to act like a taste receptor and was using the cells in its search for non-sugar sweeteners. The soft drink company has a responsible research policy which should have prevented the researchers from using HEK 293, or any other human tissue, when working for the manufacturer. There is no evidence that it was not followed. Nor is there evidence that any flavours found by the research firm have been used in the beverage company’s products.

There are clearly ethical issues around the use of embryonic cells from aborted foetuses. But there is absolutely nothing to support the cannibalism claim. Yet this idea is proliferating on the Internet. And it’s not alone. Chinese whispers are spreading like wildfire online.

So how do we determine the truth?

The best way is to research the original documents ourselves. You could, for example, read the websites of the soda maker or look at the scientific papers and patents from the research firm. But that’s time consuming. A quicker check is to see whether a web post includes links to these documents. If it does not, be suspicious.

Fortunately, there are reliable websites that will do the research for you. One is Snopes, the Urban Legends Research Page. Founded by folklorists Barbara and David Mikkelson, it has been debunking, or proving, Internet stories since 1995.

And what myths. In a recent US scam, people were chastised for missing jury duty, then tricked into revealing personal details which the criminals used to drain the victims’ bank accounts.

Others are political, such as the claim that Barack Obama’s birth certificate is a forgery. Snopes examines each element of this myth and systematically debunks it, with links to the evidence it uses.

Often, the stories are scientific, such as the claim that microwaved water is harmful to plants. It isn’t.

But sometimes, the stories are true, like the report that Irena Sendler, who helped 2,500 Jews, mostly children, escape the Warsaw ghetto during the Second World War, had lost the 2007 Nobel Peace Prize to former US vice-president Al Gore’s climate change film. Though she was and remains little known, Sendler’s heroic story is true. Check it out.