Personally, I've tried to do it with my ex-Lowrance X67 IceMachine and I had never really succeed in "flashing through ice"...unless you have clear black ice top and bottom. Once you get that layer of frozen slush/snow on top, I find the air bubbles in that white layer to throw off too much noise to read properly. Maybe it's just me...I'd like to hear what others have to say on this too.
BTW, "flashing through ice" means taking a sonar reading by placing the transducer on the surface of the ice, usually with a thin layer of water between the ice and transducer, and taking a reading of the depth without drilling a hole.
I hope he doesn't mean the pervert thing...as in taking an nude swim under the ice to surprise us all...