The phrase ‘Sul Ponticello’ written in a score means ‘play near to the bridge’. When string players play, the bow is continually making tiny adjustments, resulting in it moving nearer or further away from the bridge, according to what sonority or strength of sound is required. In Sul Ponticello however, the direction is for the bow to be as near to the bridge as possible – and this creates a harsh, metallic sound, unlike the normally warm and rich tones produced by the instrument.
A string arranger could very well write in Sul Ponticello if they wanted the effect to sound chilly, or tense. Often Sul Ponticello is written as a tremolando (rapidly repeated note) which gives the music a sinister quality and lends itself well to film or television music of a suspense / horror genre.
On a solo instrument, Sul Ponticello can sound scratchy and unpleasant, but in a whole section the effect is of a blending of sounds, resulting in an eerie and uncomfortable feel – which may well be what is required!