C# trill key   An extra tone hole is positioned to the left of the thumb key. The covering key is, like the G#, Eb and trills, normally closed and is opened by a lever usually positioned next to the ‘Bb lever’.  This key allows an easy B/C# trill and Bb/C# trill in the first two octaves (instead of using the index finger and thumb).  It also has the advantage that, on a flute with E mechanism, it can be used in conjunction with the first trill key to give an easy G/A trill in the third octave. (see also G/A trill key) The C# trill mechanism is more commonly found than the G/A trill mechanism