Unholy flip turn, p38 still does it the best though.
Secret is to keep it straight up till airspeed drops to 0, then full Rudder kick and down the other way.
Is it easy in a 109, heck no, doable, I'd say so.
As to why, if your higher, faster than the guy behind you, and you pull up into a hammerhead, and if you've judged the E states correctly. He will try to follow you up, stall, & flop, at about the same time that you do the hammer head, flip, and have him 400 below you, in your sights, full plan form shot. Ping Ping Ping BANG no more bogey.