Startle Reflex

An inherent, involuntary response to sudden or loud noise in which the neck and limbs are recoiled towards the chest. It is enhanced in individuals with high anxiety.

Reference:
Damasio, A. R., Everitt, B. J., & Bishop, D. (1996). The somatic marker hypothesis and the possible functions of the prefrontal cortex [and discussion]. Philosophical Transactions of the Royal Society of London B: Biological Sciences, 351(1346), 1413-1420. doi: 10.1098/rstb.1996.0125.