Recoil, shrink, flinch, wince, blench, quail can all mean to draw back from something, usually through fear, faintheartedness, or disgust.
Recoil more than any of the succeeding terms suggests the physical signs of such drawing back or the sensations that accompany it. The term may imply a start or a sudden movement away, but often the term suggests an inner or not outwardly apparent shaking or stirring that affects one mentally more than physically.
Shrink implies an instinctive recoil (as from something painful or unpleasant or horrible); it often implies cowardice, but it may imply extreme sensitiveness or scrupulousness.
Flinch implies a failure in resolution or an inability to overcome one’s desire to avoid or evade something that is painful, difficult, or abhorrent.
Flinch is sometimes used but wince more often when by some involuntary, often slight, physical movement (as starting or recoiling) one manifests pain, fear, disgust, or acute sensitiveness.
Blench may be indistinguishable from flinch; it often, however, carries a stronger suggestion of faintheartedness or of signs of fear.
To quail is to shrink coweringly, as from something which strikes terror.