involuntary response
- reflexInvoluntary stimulus response
- flinchInvoluntary retreat from threat
- twitchInvoluntary muscular jerk
- startleFrighten suddenly
- blinkRapid lid movement
shudder · gasp · jerk · recoil · wince · sneeze · shiver · goosebumps · heartbeat · pupil · knee-jerk · instinct · automatic · reaction · stimulus · nerve · spasm · gag