If you look at your flute, you will find that all the keys are sprung open except for D#, G# and the trill keys. The reason for this is that
Headjoints: A Guide to Choosing
The headjoint of the flute is probably the most ‘personal’ part of the instrument. A headjoint that plays well for one person may be another player’s idea of hell! For this reason, no hard and fast rules can be given as to what makes the “best” headjoint, but a few guidelines may be useful.