Early Sony plans called for the DualShock 4 to measure your galvanic skin response. Or in other words, it was going to be interested in how much you sweat.
An interview on Stuff goes into the details of the development of the DualShock 4 with lead system architect Mark Cerny. He's quoted as saying that "We had a long research project where we looked at pretty much any idea we could think of. Would it help to measure the galvanic response of the skin? We tried out a tremendous number of things - and then we went to the game teams to ask them what they thought they could use from the controller."
Skin response didn't make the final cut for the DualShock 4, but it has made me think twice about using somebody else's controller. Also, is it wrong that I now have C+C Music Factory songs stuck in my head?