JEALOUSY isn't it, some chaps fly for 40 years and can not do knife edge!!!!!! A rolling circle to them is only a dream. The sad thing is, they just think they are a little below average, they don't realize just how much skill, practise and balls this type of flying requires, ohhhhhhhhhh and i forgot reactions of a viper.
http://www.youtube.com/watch?v=GTtxStJJyFI