Trills and Composers with a Piano Background
For everybody coming from a piano background, a trill usually feels quite noisy and dragging a lot of attention on itself due to the many audible attacks of the notes that you get when you do a trill on a piano. This makes many composers coming from this instrument shy away from using trills in their orchestral music.
However there are some instruments where a trill can be an extremely subtle and just a little shimmering effect which will give a very effective sound when trying to create shimmering and “boiling” effect. On all string instruments, a soft trill will be very smooth and silky not having any of the noise that you might be used to from the piano.
But also woodwinds like the flute and particularly the clarinets (all of them) are capable of creating an incredibly subtle trill which can be used in many ways without being intrusive or attention dragging at all.