I'm guessing that hair-trigger means very responsive to input. The throttle is controlled via electronics instead of cable. In SPORT mode, since you start in first gear and there's lots of torque if the driver input is not smooth or if you are on a bumpy road and your foot comes off the gas, you will have a jerky kind of ride....In Winter mode this is not really a problem since torque is decreased by starting in second gear. Once you get used to the car (or should I say the computer learns your driving style) this is a non-issue.
Gary

------------------
http://clubs.snap.com/mercedesbenze55registry/index.lhtml
00 AMG E55
96 DCM Impala SS
94 ZR-1
81 Corvette Cpe