Startle reflex

Startle reflex is a defensive response to sudden or threatening stimuli, Sometimes when I am concentrating on a book or deep in thought about something (one of the iconic scientific images is Darwin's words 'I think' scribbled beside a tree-diagram;  my thoughts won't be so deep), if someone suddenly calls out to me, I will give a start as if a bomb has just gone off beside me. The sound won't be close to these sounds in intensity. (According to this interesting Radiolab podcast, hearing is our fastest sense.) In Laughing Gas by P.G. Wodehouse, the protagonist says:

I remember once, when a kid - from what motive I cannot recall, but no doubt in a spirit of clean fun - hiding in a sort of alcove on the main staircase at Biddleford Castle and saying 'Boo!'to a butler who was coming up with a tray containing a decanter , a syphon, and glasses. Biddleford is popularly supposed to be haunted by a Wailing lady,and the first time the butler touched the ground was when he came up against a tiger-skin rug in the hall two flights down. 

My reaction to an unexpected sound would also be as undignified as that of the unfortunate butler. My heart would jump up higher than Wordsworth's did when he saw a rainbow. It  will almost 'killofy my heart' as Epifina the bad-tempered great-grand mother of Salman Rushdie's The Moor's Last Sigh would have said. Sujit used do this often when he was smaller but he would then overdo it so the element of surprise is lost and my reactions will become normal.

A similar thing happens when slightly cold water falls on me. Sponging or any cleaning on my body is always done with lukewarm water - water that is in the Goldilocks zone: neither too hot nor too cold. I have got used to this so when normal tap water falls on me, I give a start as if ice-cold water has fallen on me.