startle reaction,
startle response a complicated involuntary reaction to a sudden unexpected stimulus (especially a loud noise); involves flexion of most skeletal muscles and a variety of visceral reactions
moro reflex,
startle reflex a normal reflex of young infants; a sudden loud noise causes the child to stretch out the arms and flex the legs
Verb
startle -
move or jump suddenly, as if in surprise or alarm; "She startled when I walked into the room"