Haha, thanks dad.
Okay, now I understand what they're doing. If there's an active snowstorm in progress, and the engines are at idle, ice can accumulate on the fans. If it gets too bad, it's throw the engine out of balance and you'll get a bad vibration in the airframe. Running the engines up simply throws the ice off of the blades and into the fan casing (it makes a pretty loud bang as its throwing the ice off at hundreds of miles per hour. We don't necessarily have to do this on the ground, but in flight if we're in icing conditions and you get an engine vib, the checklist calls for the engines to be brought to a high power setting hoping that it'll throw any ice accumulation.
I am out of training now. Had my first flight with a checkairman last week and finished up the airplane work (differences just requires me to fly 4 flights with a checkairman, then I'm done). I'm currently out on my first official trip (left Thursday, done Sunday afternoon). I'll be in/out of JFK tomorrow (sunday) bringing in a 700 from ATL and taking a 900 (which I'm completely in love with) to CVG.