Butterflying is a glitch only in Halo 2 and Halo 3. You need two people to do this and execute. In Halo 3, one person has to jump on the other's head repeatedly while the other person keeps on pressing RB and B repeatedly in a sparse repetition. It "cancels" a reload and a beat down to a lock on sequence allowing you to fly. In Halo 2, you press B and X repeatedly with an Energy Sword, but otherwise it is the same.