Consulting my copy of FBaWtFT, I’d guess the flying bug is a Billywig.
Btw, this edit is very good. (Of course Rowling is crap with screenplays and David Yates should have stuck with directing TV, but none of that is JJPotter’s fault.)
Edits are invisible, video quality is VG, and audio is stereo and upmixes well via DPLII. A couple scenes have unfinished effects, but not terribly so.