Valve has been measuring salty sweat oozing from people's pores while they play video games.
How much you sweat betrays how nervous or panicked or anxious or just plain scared you are, you see - at least that's what Valve's in-house experimental psychologist, Mike Ambinder, reckons. Like he'd know.
Armed with that data, Valve can modify game experiences on the fly. One experiment involved having people-rats shoot 100 enemies in four minutes, reported VentureBeat. If the people-rats remained calm, the game experience remained normal. But if they got nervous or aroused - started sweating - then the game would synchronise and move more quickly, giving them less time to shoot, which sounds a bit unfair.
Ambinder also said Valve had carried out eye-tracking tests - something Microsoft is rumoured to be doing with Kinect 2. A version of Portal 2 that you could control with your eyes "worked pretty well", apparently.
Other bio-bits that can be measured include things like heart rate, facial expression, brain waves (EEGs or electroencephalography), pupil dilation and body temperature.
Using those, states such as being angry, afraid, energetic, engaged, jubilant, happy, sad, bored, fatigued, passive, relaxed or content can be detected.
"One thing we are very interested in is the notion of biofeedback and how it can be applied to game design," Ambinder said. "There is potential on both sides of the equation, both for using physiological signals to quantify an emotional state while people are playing the game.
"The more interesting side of the equation is what you can do when you incorporate physiological signals into the gameplay itself.
"If we could start tapping into that, we could tap into a whole wealth of data."
Nutty professor Valve has been banging on about biometrics for a while now. Earlier this year, big boss Gabe Newell said, "I think you'll see controllers coming from us that use a lot of biometric data.
"Your hands, and your wrist muscles, and your fingers are actually your highest bandwidth - so trying to talk to a game with your arms is essentially saying 'oh we're going to stop using ethernet and go back to 300 baud dial-up'."
Yeah, that would be ridiculous, Gabe!