Cucumber moment

When you are caught completely off guard by an object that is out of place and you instinctively jump back, like when a cat sees a cucumber on the floor and jumps straight up.

'Dude, I was rushing to class today and when I turned the corner I ran up on a vacuum cleaner next to the wall. I thought it was a Dalek about to 'TERMINATE!'

'Dude, that was a real cucumber moment.'