snow-moon: we don't know means we don't know

The effects of melamine on people are thought to be minimal, but no one really knows. Its consumption by humans is considered so improbable that no one has even studied it.

~ Chicago Tribune

we are not aware of any human illness that has occurred from exposure to melamine or its by-products. While the Centers for Disease Control and Prevention systems would have limited ability to detect subtle problems due to melamine and melamine-related compounds, no problems have been detected to date. To further evaluate any potential harm to humans, the FDA is developing and implementing further tests and risk assessments based on the toxicity of the compounds and how much of the compounds consumers could be expected to actually consume.

~ FDA

When companies cook pet food, melamine and cyanuric acid could fuse into something lethal. Maybe the heat combines those two substances with yet another compound in the chow, producing deadly crystals. To test all that, he figures, you'd have to feed animals stuff that would bring activists running. "To do that kind of work," says Ebel, pondering the magnitude, "it would be a Ph.D. project."

~ Cornell University toxicologist Joe Ebel in The Oregonian

So... when you hear that "melamine is not believed to be harmful to humans" a parenthetical phrase used by CNN, the FDA, the CDC- and some Chinese farmers- remember that they have NOTHING on which to base that claim.