verb

make a sudden flinching movement out of fear or pain.

he blenched and struggled to regain his composure

flinch,start,shy (away),recoil,shrink,pull back,back away,draw back,cringe,wince,quiver,shudder,shiver,tremble,quake,shake,quail,cower,waver,falter,hesitate,get cold feet,blanch