Watch "Law & Order" for all the oh-so-obvious signs that that the killer is lying – eyes darting like crazy, shifting in the seat, sweat beads on the forehead.

Certain facial expressions also are a giveaway, though they may be harder to pick up, according to a new study from Dalhousie University in Halifax, Nova Scotia.

Researchers followed the case of Michael White, an Edmonton man convicted of killing his pregant wife - Canada's version of Scott Peterson. He initially generated a lot of public sympathy with his tearful pleas for help in finding his wife.

But in an analysis of White's T.V. appearances, frame by frame, researchers found traces of anger and disgust – so fleeting that many in the public never noticed.

Researchers went on to test subjects in the lab. They were showed images that elicit happiness (puppies frolicking), fear (open-mouthed rabid dog, a close-up to boot) and ewwws (a severed hand), and videotaped subjects' reactions.

The researchers' findings, published in Psychological Science, showed that happiness is easier to feign than fear or disgust. But none of their subjects were able to fake their feelings perfectly.

Researchers said certain facial muscles cannot be controlled, and that some muscles are not activated in the absence of genuine emotion.

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