If a violinist who is playing in just intonation, as in the chart I linked to, plays a G# in the context of being the major third in the key of E major, they will pitch the note 13.69 cents higher than it would be in equal temperament. If they play an Ab in the context of being the minor third of F minor, they will pitch it 15.64 cents lower than its equal tempered counterpart. So, on a violin playing in just temperament, G# and Ab are about 5mm apart, 29.33 cents, or just under a third of a semitone. They are both just less than a sixth of a semitone 'out of tune' with the note which would be played in E major or F minor on a fixed pitch equal tempered instrument, but on the violin they would sound distinctly more major or minor. I find that difference clearly audible. Consequently, violinists need to be kept under strict control when in an ensemble situation involving fixed pitch instruments. Judicious use of a cattle prod can be beneficial, as can kicking.